I have an IIS 6 server serving an application using a mix of classic ASP and ASP.NET.
I'm increasingly getting problems where the number of requests in the ASP.NET requests queue (observed using the ASP.NET\Requests Queued counter) starts to increase to a point where the server can no longer service the requests. That happens a three or four minutes from the point where queued requests starts increasing. Recycling the application pool restores service.
Normally, requests queued is zero and occasionally there'll be small spikes but it seems that once or twice a day, a number of requests are blocking the queue and queued requests starts to increase.
I suspect there are network problems causing clients to lose their connection (and re-submit their request) and the requests in the queue continue despite losing their client.