Scalability is a daily concern on my business. We managed thousands of requests, that startup lots of transactions that will make any online bank website simply jealous.
A couple of times, I worked with companies that use ASP.Net as their web framework of preference and it was not long when we start having scalability problems. It is a well known issue with ASP.Net, but there are solutions.
I found this interesting article that talks about the issue and gives a good solution.