Some time ago the forth alpha release of the new ubuntu 6.04 came out. Yesterday I installed it. Installation went good, no troubles at all. When I logged in I had a flickering screen so I had to change the modelines (same thing in 5.10). First I looked for nvidia drivers,
apt-get install nvidia-glx
and then enable it in /etc/X11/xorg.conf
I also had no mp3 support, even with gstreamer0.8-mad. This is because the new Ubuntu uses gstreamer0.10. The plugins you need are in gstreamer0.10-plugins-ugly. This also enables mp3 decoding in Serpentine
apt-get install gstreamer-0.10-plugins-ugly
Almost all apps are improved, rhythmbox got a new UI (though I still like amaroK better), gedit got lots of new stuff, especially for pythoneers, firefox 1.5 is included, the new evolution beta, a improved version of Xchat etc. etc. etc.
The biggest improvement is imo the gnome 2.14 beta. It's boots up a lot faster (imo) and lots of bugs are fixed.
Ubuntu Dapper Drake Flight 4 rocks!
for more info and downloads : https://wiki.ubuntu.com/DapperFlight4