I have been a WordPress user now for over 4 years, and I have never such a total disaster with 3.5.1
Why would WordPress make such a huge change is how images are handled. As photographer, it's key that I be able to work with images in almost all of my posts.
On upgrading to 3.5.1, I find that I am unable to work with media as before.
1. On a standard post, where you would hit add media, when you hit hit this now, nothing happens.
2. If you go to the media tab and try to add media there, it works, but you now have almost NO control over the file. In pat wordpress versions, the user was able to have much more control over the image. If you hit edit now, again nothing happens.
3. Existing portfolios that worked fine in the previous version of wordpress, now no longer show any thumbnails, with any of the themes I have used. Yet you can go to the media library and see that a particular media file is linked to a portfolio.
I don't understand why anyone would find this as a positive development of wordpress, i.e. basically nothing works now with images as it did with past versions. I would feel that a warning might be needed. Thankfully I had a beta site and was able to test this and it did not harm my main production sites.