Ever since I upgraded to 2.7, on both of my domains, I've been unable to successfully upload pictures into my blog entries while writing them. Clicking the "upload image"-link - or any of the four Upload/Insert links, really - navigates me away from the blog entry editor and into a new page, instead of opening a small window on top of my editor.
If I chose to upload the picture anyway, the "insert image into post"-button leads me to an empty page, not back to my post.
I've noticed a similar problem when I add an image manually. Clicking the image in the Visual editor and clicking the "Edit Image"-icon puts a dark grey cover over the editor as it did in 2.6, but the actual Image Editing window doesn't show up over it.
Before you ask; I upgraded to 2.7 by replacing _all_ files in my installation, overwriting everything, not just the newest files. I've tried clearing the cache, run different browsers and emptied the /wp-content/uploads/js_cache