Recently launched an ASP.NET site running on a single 32-bit WS2003 box (SQL on a separate server). The server has 4GB intalled, 3GB available. According to task manager, the w3wp.exe process is only using between 200-600MB. The site has tens of thousands of pages and makes heavy use of page output caching, so I would expect it to use a lot more of the available memory.
The app pool isn't set to throttle memory usage. Is there anything else that might be limiting the amount of memory that IIS takes?