I've never seen this before and none of our customers have ever reported it to us either. According to Microsoft (MS):
"To put it simply, the queue length is NOT the number of concurrent requests a particular app pool can handle. It is only a precautionary measure to prevent the server from falling too far behind in processing requests."
But it does look like you can modify this setting. This blog
(albeit about Exchange) talks about modifying the setting in IIS. It looks like Microsoft doesn't recommend increasing the queue to over 10,000. There is another article here
that has a few more details. If you do go the route of increasing the queue, can you post your results? Since this is the first time we've heard of this it would good to see the impact and/or results that happen when modifying this setting.