Nothing special with Windows 7 64 bit.
except of course if you need to memory address more than 2^32 (4GB). I commonly use more than 5GB when encoding, mounting dvds to play or install, gaming etc etc.
I have a 1GB graphics card, 6GB RAM, 60Mb of sound card memory and other memory. The total is over 7GB. Using a 32bit OS would mean i would only be able to address 2.5GB system memory (RAM) for the OS. This is why a 64bit OS is recommended. Gone are the bad old days regarding drivers etc.
What this also means is that if i only have 2.5GB i will be relying on a thrashing hard driver or a slower ssd to get that info instead of RAM, this is not a good idea. 2.5GB doesn't take much to use if you are a power user. You never know when you might want to use more.