I installed Ubuntu 9.04 a few weeks ago from a free CD I got in Linux Format magazine. I started upgrading it to Karmic 9.10 at Alpha 2.
I did all the Alphas, then upgraded to Beta and the RC, finally to the Final Release. There were glitches in the Daily Builds, especially the closer I got to the RC of Karmic. But nothing major; small annoyances. Everything seemed to get worked out in the Release Candidate on the last week before 9.10 was released as Final. I have been using Ubuntu Karmic Koala 9.10 off-and-on with no problems, at all.
I have been changing things and customizing the heck out of it. It seems to be a well thought out and put together Distro. The many Ubuntu Devs did a good job. Although, supposedly, it is the fore-runner for Ubuntu's Lucid Lynx 10.04 which will be the new Ubuntu LTS distro, this coming May 2010.
Because of my love of the Xfce interface, I also, downloaded Xubuntu 9.10 via Torrent a few days after it's Final release. Again, a nice distro with no problems that I can see.
I'm looking forward to see what the Mint Devs will do with Karmic 9.10 and the improvements they will make in evolving the next Mint-8. I trust Clem and the Mint Team to do a great job in making Helena-8 a great distro. I want to try-out both LinuxMint-8 (gnome) and LinuxMint-8 Xfce CE when it becomes available. I'm a hard-core LinuxMint Addict.