I don't think London is getting that much rail instrastructure for the Olympics. The London Overground is certainly new, but it's mostly a reorganization of services that have run for decades, and the newer piece isn't particularly advantageous for the Olympics - and the piece they are currently building to comlete the link around London doesn't open until after the Olympics as far as I know (nor was it planned to). There's certainly some new DRL services near the Olympic site that have been driven by the Olympics - but it's very much like grade-separated LRT rather than heavy rail. The newish Jubilee line will be essential, but it was already open when they started bidding. The high-speed rail connection from the Olympic site at Stratford International to St. Pancras and Kent will be specially operated for the Olympics, but only the station is for the Olympics, the HS1 line itself was under construction long before the Olympics were awarded.Well, I'll say this, if an Olympic bid results in the GTA getting our own version of the Overground and other rail links London's getting for 2012, then I can swallow that bitter pill.
The biggest project going in London currently is the Crossrail line - essentially a huge subway under London - but it won't open until long after the Olympics. There's been no tube expansions for the Olympics