I’ve had similar problems after upgrading to 3.1. Javascript was causing problems in admin area, e.g. edit post button and insert image buttons weren’t working. Disabling all plugins didn’t help.
Then I discovered a strangely named directory in wp-content – “…” – that is three dots for the dir name. After I checked it’s content, it seemed as some plugins were using this directory as cache or backup. After deleting the directory “…” and deleting the browser cache everything started working. I didn’t find such directory on my other WordPress sites.
Maybe worth mentioning: the server was hacked a few months back and it’s admins installed a bunch of WordPress security plugins. However, WordPress wasn’t the issue, it was a case of stolen FTP passwords, but those plugins remained installed. Here’s a list of all installed plugins:
Akismet
AntiVirus
Configure SMTP
Contact Form 7
Event Calendar
Event Calendar Widget
Flexible Lightboxe
Google Analytics for WordPress
New Tag Cloud
Really Simple CAPTCHA
Scissors
WP Security Scan
