PSD Viewing and Diffing
github.com
github.com
That's what PSD Native is for: http://layervault.tumblr.com/post/82315160104/psd-rb-and-psd...
More information than you ever wanted about Adobe file formats: http://www.adobe.com/devnet-apps/photoshop/fileformatashtml/
I just wish PSD files weren't so horrendously, horrendously, horrendously, terrible with space.
Our design people routinely have to deal with 300MB+ files for client work. I'm not convinced yet it's worth the benefits if the only way they can work w/git(hub) is with git-bigfiles or git-annex, or some convoluted custom workflow =(