If you can get past botched upgrade or troublesome fresh install of Ubuntu 9.10, as many have experienced, this is the single most important Ubuntu released yet. I mean, all new Ubuntu releases are supposedly better than the previous version, because they come with new versions of popular packages and bug fixes of the older version of this popular distribution. But with karmic Koala, Canonical introduced features like Ubuntu One and Software Center, that are truly big new features. More so, when you consider the fact that Ubuntu releases a new version every six months.
Unfortunately, most of the good vibe with new version of Ubuntu got lost when users started reporting problems with upgrading from Jaunty and for many, even on fresh install. Reports are still coming in, but the official Ubuntu IRC channel and Ubuntu Forum is flooded with troubleshooting questions from early adopters. Most of the problems seems to be related to graphics driver and Wi-Fi connection dropping out randomly. Others are having trouble to even boot up to X.
Personally I have installed in three computers with mixed results and ironically the only install that went smooth was my install on a Macbook.
For anyone thinking about upgrading to 9.10, I suggest wait couple of weeks when most of the kinks should be ironed out. Otherwise do a clean install on a test machine of a separate partition to see how it goes. Many have reported trouble-free upgrade and fresh install so you might not have any problem at all. Hopefully, this is a small hiccup on an otherwise very impressive Ubuntu release.