I've written about how the 4GB 32-bit Windows memory limit impacts Terminal Server environments. That article has spawned a lot of discussions, particularly about whether 64-bit environments will have the same limit.
Microsoft has actually published a KB article comparing 64-bit and 32-bit memory architectures. Here's a snapshot of the major differences:
|Page file size||16TB||512TB|
|Page Table Entries||660MB||128GB|
I think it's safe to say that when we move to 64-bit Windows, we won't have to worry about running out of kernel memory space for 10 or 15 years!