I upgraded from 2.3.3 to 2.5. I replaced all files except wp-config.php. When I went to mysite.com/wp-admin/upgrade.php, it says:
No Upgrade Required
Your WordPress database is already up-to-date!
I go to admin and find that my blog site looks the same. I try writing a post and it's ok. When I insert an image or a video, that's where i find error. Neither of the two appears.