ick, I don't think I could stand living in London myself. I mean I love the tube and the shops etc but it always just seems too big, too anonymous or something. One of my friends rejected his Clare offer the year I went to go to Imperial, despite the fact I thought he'd love it at Clare, and now he's having a brilliant time at Imp... so I guess it really doesn't matter much where you are as long as you make the best of it. Which I'm sure you will!
Where are you considering from the other places you applied now?
There is always that, it's probably a good idea to still get As (I'm still battling with my lazyness - was the worst compsci in my year at the last exams
- need to do better this year
). It'll probably be a lot less stress in August too, I was a lot more stressed then than with the offer letter believe it or not - I barely talked to anyone for two days beforehand! (that did make the pub afterward all the more fun though!)
I guess your course where ever you end up will also be easier... which leaves more time for other cool stuff!
To give you a little perspective, I know 6 people from my year at school who were rejected by oxbridge - there was only one who was particularly annoyed after some time had passed and that was because they'd taken his girlfriend but not him! Everyone else seems to be enjoying themselves - I guess it's such a massive change in your life you forget where you thought you might be because you're too busy having fun or something!