I installed Ubuntu 8.04 last week. The first impression was not good since it hangs after initial bootup. This reminds me of OpenSuse 10.3 after enabling compiz. So I boot into Gnome Fail Safe Session and disabled Visual Effects (and actually removed compiz) and then reboot. This solved the problem.
Other than this initial glitch, it seems to be quite smooth and solid, not like the initial bump with Ubuntu 7.10 (7.04 was flawless, 6.06 is solid). I was able to set up my usual testing environment and build various PIC or USB related programs from the CVS/SVN source pretty fast and all of them seem to work fine.
On the other hand, there are no nothing too special with Ubuntu 8.04. Maybe this reflects my simple usage pattern with Linux.