If you're using any plugins that affect commenting, then you'll have a problem unless they were updated for 2.7. Same thing for stuff that affects the admin panel. Other than that though, no problems.
Bloated and slow. Lots of code bloat for nothing. I am going to look into django or some other software. WP is heading in the wrong direction. Used to be lite and fast, not anymore.
I just updated all my Wordpress blogs to 2.7 including the one in my blog feed. I can't understand why: a) There are updates every few weeks.. b) Why their design (admin) has become so loaded... It might only be a short upgrade but logging in to FTP, uploading files, config file updates, etc. etc. just take way more than simply a few minutes!!
User CP, Edit Options, scroll down to the bottom of the page and you'll find the spot to enter your XML feed.