Karmic's great
Not so sure it's such an order of magnitude of improvement over Jaunty, but it does improve quite a few things greatly. The lack of a kde-based grub editor was a a bit of a shock, however, and the change to grub 2 is scary, especially as the configuration files have changed.
On the up side, my webcam now works, even if the microphone doesn't (Skype is, therefore, still text only for me unless I reboot into XP).
I started with the beta and have just been using the distribution upgrade, something I've had trouble with in the past... it's been working fine every time I've used it since a reinstall.
I still keep XP about for some apps I can't run under Linux yet, but I find that for general usage - Internet, word processing, games, more or less everything really - that I tend to boot into kubuntu because of its speed. I re-ghosted back to XP because Vista felt so slow, even with 4GB of RAM installed... and even the Windows 7 release candidate feels sluggish and bloated compared to karmic.