Markus Frind has posted his experience of using ASP.NET 2.0 for one of largest dating site PlentyOfFish.com in Canada. In his post, Markus is telling how he has addressed concurrency issues by switching to ASP.NET 2.0:
At this point there were a lot of concurrency issues, the site would slooow down and just keep getting slower as more people came on. After switching to asp.net 2.0 all those problems went away. Now when there are over 32,000 concurrent connections at peak the site does not slow down. There are however still problems. I find that once you pass 100 Pageviews/second threads timers start to not get called for no reason.
Interestingly, he didn't use any kind of caching to render pages. Every page hit actually pull content from database.