I have replaced the SSD in my 64GB Surface Pro. It has been an adventure and I'm still having trouble with the 256GB SSD. I'm hopping to have Win8 reinstalled sometime today. You can see pictues and follow my findings on the Microsoft forum at tabletpcreview in the thread "Anyone try opening up there pro yet"
http://forum.tabletpcreview.com/microsoft/55362-anyone-try-opening-up-their-pro-yet-5.html