I think the defensive steps taken for the 2012 Olympics are just a bit over the top.
Do they expect to discover a flight of stealth bombers coming over the horizon to bomb London? Or is just a good chance to show off to the world and to the citizen’s of the realm? Nothing wrong with that but it would be a bit uncomfortable to have a missile site on your roof-top.
The most likely attacks would be against soft targets, the Tube and the buses, that will be moving thousands of people a day to and from the Olympic venues. It is always hard to defend against idiots willing to perform a suicide mission. Look at the last London bombings. Those idiots (most from Pakistan) had wives, children and unborn children they were willing to part with as “soldiers” in the fight against infidels.
Let’s hope and pray that all goes well and that all are safe.