I just upgraded my wordpress (2.1.2) to 2.2 today. I first did the upgrade on a test box that I have (running FreeBSD) using the tar.gz download. Everything went fine with the update.
I then used the .zip download of 2.2 to upgrade my production server (this because the desktop I was using wasn't able to decompress tar.gz). I noticed after doing that update that the rss2 feed showed my previous version at the top (generator="wordpress/2.1.2"). I then used the tar.gz download and upgraded again. This time the top of the rss2 feed was showing the expected information (generator="wordpress/2.2").
I hope this isn't an indicator of any other differences between the tar.gz and .zip downloads. Has anyone else had issues with this or noticed any differences between the downloads?