I just updated my WordPress installation from 3.2 to 3.3. The upgrade was running but then the page directed to this message:
Briefly unavailable for scheduled maintenance. Check back in a minute.
The front page and wp-admin both showed this unstyled message. After a quick search I found that simply deleting the .maintenance file via FTP will remove this. Perhaps it’s a bug in this version, perhaps something went wrong. But after deleting that file everything seems to be working well. And I must say I like the design tweaks in WordPress 3.3.