It is not just a Mepis problem. Anyone using a distro that is heavily dependant on Debian (as you know Mepis is 90%+ debian and it wants to stay that way - unlike Ubuntu with its own packages) will just have to be patient when it comes to upgrading at the moment until Debian gets things sorted out.
Mepis 3.4 is supposed to be the one with "major" changes, ie KDE 3.4, possibly xorg, blah blah blah.
Relax - why hurry to download such minor changes and possibly (the key word here) mess up your system.
Why not mess around with the kanotix distro to see various changes? I've done a little bit, knowing I'm safe leaving my Mepis 3.3 well alone.
Edit: See this official announcement here:
Are you are suspicious that there will be problems upgrading from 3.3 to 3.4?