I just downloaded and installed WordPress 2.7 RC1. The upgrade took about 3 minutes, end to end, and the “several moments” database upgrade took less than 2 seconds. All in the all, there’s very little to notice on the front end that is different, I haven’t been able to test comment threading yet. However, the new admin site is really nice looking. The Dashboard is a HUGE improvement over the <2.7 series.
Themes were entirely unbroken. Upgrading firsttube.com may be a bit more of a challenge since I’ve manually changed a few fore WordPress files, which may prevent in place automatic upgrades. However, all in all, I think the 2.7 release is looking really great.
When 2.7 final is released, I expect to be updating my live site pretty quickly.