Ok so i updated to 3.5 yesterday and now my insert media in the post/page editing area doesn't work anymore.
When i click the button, the overlay opens but i don't see any pictures in the media galery and when i try to upload an image i get "Error. Please try again later". However the picture does get uploaded. If i access the Media library from the side bar i can see the picture there.
Also the wordpress admin bar, side-bar and footer are gone. I checked the code and it's there ... I don't know if this is related but maybe it helps.