Comment 4 for bug 542404

I'm in the middle of experiencing exactly the same problem. To answer Pedro's questions I can provide the following information:

1. the specific steps or actions you took that caused you to encounter the problem.
Upgrading from karmic to lucid. Manually changed all occurrences of karmic to lucid in /etc/apt/sources.list (see bottom of comment).
On the command line, performed:
$sudo apt-get update
$sudo apt-get dist-upgrade
Once upgrade was complete, restarted the computer.
Presented with login screen, no gnome desktop environment available, only xterm.

2. the behavior you expected
Gnome to still be present. Along with nautilus and the rest of the environment.

3. the behavior you actually encountered (in as much detail as possible).
Gnome was not installed, nor was nautilus. "$ apt-get install nautilus" succeeded as expected.
when I perform "$ apt-get install gnome" I get the following information:

Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
  gnome: Depends: swfdec-mozilla but it is not going to be installed
E: Broken packages

I can then perform the following:
$ sudo apt-get install swfdec-mozilla
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  w3c-dtd-xhtml
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  libswfdec-0.8-0
The following packages will be REMOVED
  epiphany-browser epiphany-extensions
The following NEW packages will be installed
  libswfdec-0.8-0 swfdec-mozilla
0 upgraded, 2 newly installed, 2 to remove and 0 not upgraded.
Need to get 0B/471kB of archives.
After this operation, 2,683kB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 243291 files and directories currently installed.)
Removing epiphany-extensions ...
Removing epiphany-browser ...
update-alternatives: using /usr/bin/firefox to provide /usr/bin/x-www-browser (x-www-browser) in auto mode.
update-alternatives: using /usr/bin/google-chrome to provide /usr/bin/gnome-www-browser (gnome-www-browser) in auto mode.
Processing triggers for man-db ...
Selecting previously deselected package libswfdec-0.8-0.
(Reading database ... 243025 files and directories currently installed.)
Unpacking libswfdec-0.8-0 (from .../libswfdec-0.8-0_0.8.4-1build1_i386.deb) ...
Selecting previously deselected package swfdec-mozilla.
Unpacking swfdec-mozilla (from .../swfdec-mozilla_0.8.2-1ubuntu2_i386.deb) ...
Processing triggers for hicolor-icon-theme ...
Setting up libswfdec-0.8-0 (0.8.4-1build1) ...

Setting up swfdec-mozilla (0.8.2-1ubuntu2) ...
update-alternatives: using /usr/lib/swfdec-mozilla/libswfdecmozilla.so to provide /usr/lib/iceape/plugins/flashplugin-alternative.so (iceape-flashplugin) in auto mode.
update-alternatives: using /usr/lib/swfdec-mozilla/libswfdecmozilla.so to provide /usr/lib/iceweasel/plugins/flashplugin-alternative.so (iceweasel-flashplugin) in auto mode.
update-alternatives: using /usr/lib/swfdec-mozilla/libswfdecmozilla.so to provide /usr/lib/mozilla/plugins/flashplugin-alternative.so (mozilla-flashplugin) in auto mode.
update-alternatives: using /usr/lib/swfdec-mozilla/libswfdecmozilla.so to provide /usr/lib/firefox/plugins/flashplugin-alternative.so (firefox-flashplugin) in auto mode.
update-alternatives: using /usr/lib/swfdec-mozilla/libswfdecmozilla.so to provide /usr/lib/xulrunner/plugins/flashplugin-alternative.so (xulrunner-flashplugin) in auto mode.
update-alternatives: using /usr/lib/swfdec-mozilla/libswfdecmozilla.so to provide /usr/lib/midbrowser/plugins/flashplugin-alternative.so (midbrowser-flashplugin) in auto mode.
update-alternatives: using /usr/lib/swfdec-mozilla/libswfdecmozilla.so to provide /usr/lib/xulrunner-addons/plugins/flashplugin-alternative.so (xulrunner-addons-flashplugin) in auto mode.

Processing triggers for libc-bin ...
ldconfig deferred processing now taking place

and trying to install gnome again results in:
$ sudo apt-get install gnome
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies.
  gnome: Depends: epiphany-extensions but it is not going to be installed
E: Broken packages

As another poster commented, I have tried changing my sources to point to "main", and moving to different mirrors, uk and us, none of which has been successful.

My sources list is:
$cat sources.list
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.

deb http://gb.archive.ubuntu.com/ubuntu/ lucid main universe restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid main

## Major bug fix updates produced after the final release of the
## distribution.
deb http://gb.archive.ubuntu.com/ubuntu/ lucid-updates main universe restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid-updates main

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://gb.archive.ubuntu.com/ubuntu/ lucid multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid multiverse
deb http://gb.archive.ubuntu.com/ubuntu/ lucid-updates multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid-updates multiverse

## Uncomment the following two lines to add software from the 'backports'
## repository.
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://gb.archive.ubuntu.com/ubuntu/ lucid-backports main multiverse universe restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid-backports main multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu lucid partner
deb-src http://archive.canonical.com/ubuntu lucid partner

deb http://gb.archive.ubuntu.com/ubuntu/ lucid-security main universe restricted
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid-security main
deb http://gb.archive.ubuntu.com/ubuntu/ lucid-security multiverse
deb-src http://gb.archive.ubuntu.com/ubuntu/ lucid-security multiverse

deb http://ppa.launchpad.net/anders-kaseorg/subversion-1.6/ubuntu lucid main
deb-src http://ppa.launchpad.net/anders-kaseorg/subversion-1.6/ubuntu lucid main
deb http://gb.archive.ubuntu.com/ubuntu/ lucid-proposed universe main multiverse restricted
deb http://packages.medibuntu.org/ lucid free non-free
deb-src http://packages.medibuntu.org/ lucid free non-free

# Google software repository
deb http://dl.google.com/linux/deb/ stable non-free

deb http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu lucid main
deb-src http://ppa.launchpad.net/ubuntu-mozilla-daily/ppa/ubuntu lucid main

deb http://ppa.launchpad.net/rabbitvcs/ppa/ubuntu lucid main