So I decided to have a look at the bleeding edge and try out the media uploader. It's completely broken on my shared hosting, but works beautifully on my local install. I tried it with a fresh install of the beta with no plugins and only Twenty-Twelve - fresh out of the box! Here is what's broken:
1) When I upload an image or several images using the new media uploader, I can see the progress of the upload(s), but when they are finished, I am sent right back to the "Select Files" screen of the Modal, rather than having a chance to edit the metadata of the image(s)
2) I can see that the images are located in my upload folder, but when I tried to insert in the post, I had a 50/50 chance of the image being a "broken link" in the post editor
3) If I go to the media library, I can see the thumbnails of all the images I uploaded; however, if I go to edit the image and it's metadata, I do not see the image, and if I click "Edit Image" on the "Edit Media" page for that image, I get "Image data does not exist. Please re-upload the image."
So that's a quick summary of my issue. The only difference I can see between my live site and my local dev is that local dev uses PHP 5.3.1 whereas live uses 5.2.17. Would that be the problem? Or could it be something else? What can I do to help track down what the issue is?