I was most intrigued by the ending with you-know-Who (dont want to spoil it for anyone who hasnt seen it yet) and his comment about revisiting familiar faces or something like that. This leads me to believe that at some point the Doctor will get the ability to regenerate into previous incarnations of himself.
Don't worry; it's aired, and if anyone has made it 7 pages into this thread, they're well and truly spoiled already!