Yes, overcrowding at all stations within central London and outwards to the Olympic Stadium in Stratford! Do not expect to go anywhere fast, road, trains, foot paths will be very busy.
Hotel/Accomodation will be at a Premium with some rented houses near the olympic sites being as much as 2000 pounds a week.
If you wish to come during this season, aim for after the olympics not before, everything should quieten down. about 6 years ago
There are going to be hundreds of thousands (millions?) more tourists in London for the games. Tourists attract petty thieves. It's like a honey pot for them, so be extra vigilant about keeping a hold of your bags and wallets.
Heathrow (and other border entry points like the Chunnel) are presently experiencing long delays because of a lack of staff. Up to 3 hours or more at Heathrow. The government is promising they'll have more staff for the Olympics but don't hold your breath - expect LOOOONG delays and lots of waiting at immigration/border control.
There's always concern the games will be targeted by terrorist groups, because in the past they have been. But on the other hand the anti-terrorist forces are on high alert. Security at venues will be very tight. So tight that inside a stadium during an olympic event is probably the safest place to be. It's outside official venues, at all the 'popular' spots outside of the control of the Olympic officials that you're most at risk.
There's talk of a repeat of the London riots. It's my observation that there's always talk like that, but not much eventuates.
It's also my experience of the Olympics here in Sydney in 2000, that everyone gets into the spirit. At events you'll be surrounded by happy sports-loving people who are trying to have as much fun as you are.
It's a risk (as is everything in life) but a calculated risk, and I personally believe that as long as you take appropriate precautions, the benefits outweigh the negatives.
Phil, travel safety specialist at TID about 6 years ago