I have 2008 R2 server where I run Microsoft Exchange 2007. I noticed that the server was running very slow so I checked the task manager and I realised that one intance of w3wp.exe was taking all the resources. I tracked the instance to be related to the MSExchangeSyncAppPool. As soon as I stop that app pool the server goes back to "normal".
I've tried adjusting "Recycling" and other options in the same category but nothing helps.