Brace yourselves for a long wait boys and girls! I was given a conditional offer for the MPhil REF at Cambridge last year. Application was received in the beginning of December and the offer was made in June. So about a 6 month wait...
Its not a quick process by any means, so start thinking long and hard about your chances of getting into Cambridge, and how badly you actually want to go there, in comparison to your other offers.
That said, maybe the waiting process isn't as long for all applications but that's just my experience so hope it helps someone a little bit. I know it's a pretty tough time with all the waiting and not knowing.