I actually...
...quite surpised myself by liking Donna. I was expecting her to be either just like she was in the previous Xmas special (i.e. infuriatingly shouty and annoying), or that we'd get a series of "Do I look bovvered?". But she actually turned out to be one of the best companions by a) NOT being all gooey about the Doc, and b) challenging him all the time to re-think his position on things.
As for the Doc's regeneration, there's going to be some wonderful Deus Ex Machina that RTD has thought up. My money is either on the hand, or Rose opening the heart of the TARDIS - she opened it once, and it's linked to psychically or somthing (insert usual complicated reason here) - and most of the Doc's regernation energy is sucked in, leaving just enough to heal him but not change his appearance.
However, the "Time Beatle" theory is out. The frizzy-haired one definitely said "There WAS something on your back", not "There IS something on your back".
Mine's the one inside the blue police box with "Bad Wolf" written on the door...