Having finished my late session today, there was absolute transport chaos as they did a 'live' rehearsal of the opening ceremony with every seat occupied and then a mass exodus to the public transport system to stress-test their plans. Unfortunately several of the undergound trains decided to break down for real so by the time everyone left, the existing systems were backlogged too - some 10,000 still stuck there apparently!
You can see the buildup of people being held back at Stratford Train/Bus station until any trains, underground and additional buses could come to help get everyone back and get people to new routes to get around the closed lines - quite amazing scenes really and fortunately everyone showed great patience, because a stampede would have been disastrous.

Hopefully the transport systems won't have any breakdowns or line closures on Friday, but if it does well I suppose they have already rehearsed that aspect too.
It should be amazing on Friday as the world watches too, but I wouldn't stray far on the public transport system on Friday if travel isn't essential - it will be swamped!