Response.TransmitFile + Close will kill your application

Just before last weekend I noticed that a website I'm responsible for started spitting out "Server is busy" messages, not something you want to see on a website with millions of visitors per day. The quickfix was to recycle the application pool, and thus I solved the symptoms by setting a 15 mins recycle cycle on all the application pools. Not exactly optimal, but sometimes pissing your pants is the way to go.