If you have big applications the 4GB limit can become an issue. I wouldn't bother if your app doesn't hit this limit or your machine doesn't have more than 4GB of RAM. Sooner or later 64-Bit will become more and more compelling, especially when you do virtualization or Shared Hosting.
For IIS7 Shared Hosting scenarios we recommend running a 64-Bit Longhorn OS with 32-Bit worker processes. This will give the OS the full 64-Bit address space and IIS worker processes stay small because they are still 32-Bit. 64-Bit apps are always a bit bigger because all pointers are 64-Bit (8 bytes) instead of 4 byte now. This means there is no way around using more RAM when your app or OS is a 64-Bit.
Hope this helps