The Olympics are already in full swing and, this being 2012, they're going to be the most "connected" event in history. Everyone is carrying a smartphone and everyone is using it. Which is great for those feeling the need to tweet or post a photo of what they're doing or seeing every other second, but not so great for everyone else needing some bandwidth, especially when "everyone else" means equipment used in some of the Olympic events.
It's such a problem, apparently, that the Olympic Committee has asked people attending the games to keep it down, i.e. stop tweeting and texting so much. It's not a ban by any means, but the OC would really appreciate it if you sent fewer tweets.
Apparently, so many people are using their phones so much during the men's cycling road race that the GPS devices installed on the bikes couldn't send their positioning data leaving commentators without much info on the ranking at any given time.
Why were the GPS devices using public networks for this is another question. It's obviously the easiest solution, but it's also the most prone to problems.
Any large gathering of people is going to put a strain on the existing cellular network, which is designed to handle a certain number of phones for any given area and that number is based on how many people are likely to be using phones in that area.
Any special event, like a concert, or an Olympic race as was the case now, is going to get together a lot more people in a place than usual.
In fact, even with people not tweeting or texting more than usual, the network should be flooded. But the major carriers and ISPs all assured people that they took measures to deal with the influx of demand caused by the Olympics.