I just upgraded this blog to WordPress 2.2. The only issue that I ran into was that the Category Cloud widget didn’t work until I upgraded from 1.1.1 to 1.3. Otherwise, it was completely painless: deactivate plugins, unpack the distro zip on top of the existing files, run the upgrade.php script, and reactivate plugins. ((Remembering to jot down which plugins I was running before the upgrade…)) No, I didn’t make a backup, although perhaps a zfs snapshot would have been prudent….
As to the new features: having sidebar widgets built-in is nice, and the drag-and-drop widget editor now works properly in Safari. On the other hand, I’m not sure about the new preview mode: it’s more accurate, but I miss having the HTML and output on the same page. We’ll see. Having full ATOM support is most welcome, and overall I think that 2.2 is a clear step forward.