Windows Server has a nice little CScript application called IISAPP that makes it nice and easy to differentiate w3wp.exe processes that are running. By calling this script in the command line you can get an output that shows the process id and the app pool. So if, by chance, you need to attach to a process to debug a new SharePoint feature – you don’t have to attach to them all – you can find the right one.

More info on IISAPP on TechNet