I noticed huge (~ 500 Mb) usage of memory on my workstation running on Ubuntu 9.10 (on amd64), causing issues when running large numerical numpy scripts. It ended up being related to ureadahead.
Removing ureadahead, and rebooting seems to fix the issue for now. I am baffled such a bug stayed in a release version. It seems that every new version of Ubuntu is slightly worse than the previous one. It is still better than many other low-hassle distributions, but I worry about the trend.
Nothing to say 
Yeah, Karmic seems to have a lot of little bugs, but I haven’t run into any lethal ones yet. Unfortunately, Fedora seems headed in the same direction. I think they are pushing too close to the bleeding edge and going for glitter (fast boot) over stability.
Time to move back to Debian? Maybe Ondrej was right all along :)