So I've tried everything in this thread: http://wordpress.org/support/topic/25-imagemedia-uploader-problems?replies=1
I've had no luck. Basically, whenever I try to add an image/video/etc to the media library, whether through the library directly or from within a post/page, I encounter problems. I select my asset and hit upload, and the progress bar shows that the asset is uploading, reaches 100% and then any indication that i uploaded something is gone. This happens whether I use the Flash Uploader or the Browser Uploader. The assets are actually making it to the server though. If I ftp into the uploads directory, they're there, but they aren't getting processed by WordPress as far as I can tell, because there's only the original file, not the resized file for thumbnails.
I haven't been able to come across any other thread on here where someone is encountering these issues but the file actually makes it to the server. Any suggestions?