There's a lot of talk in London about the legacy of the games. I think it's now firmly established that no city which has previously hosted the games has seen a long term economic benefit. Why should London?
Another aspect of the story in the UK is that we want children growing up to play sport. I gather that a lot of poorer schools don't even have playing fields, and there is a huge disparity between state schools and private schools.
I can't imagine the 2012 Olymipics having a lasting legacy when the only sport on free to air TV these days is football and cricket. The social cut off will always be those who can afford cable and those who can't. I was lucky. I grew up watching sport on TV and I could understand and appreciate a range of sports. We played a range of games in school, though it being New Zealand there was an emphasis on rugby.
When 25% or so of the population earn below the minimum wage + 50p per hour, who is able to afford cable TV in order to watch sports these days? The local pub has cable sport but mainly shows football or very occasionally rugby.
So yes it's great watching people excel and seeing how each person is supported by a team of coaches and physios etc. And but that is going to be over in two weeks and we'll be back to a monotonous diet of over-paid morons kicking a ball around, and 5 day cricket matches in a time of increasingly short attention spans.