Two words: Disk Cache
I have 32 gig of memory on my system. 16 wasn't enough, i was running out of memory. with 32, I have an 8 gig ramdisk which I load my games onto (I'm only actively playing one at a time, so if I switch games, I load another). While I don't need it because of extremely fast D drive (RAID 10, 8 drives) and an SSD C drive, a good disk cache is also useful in reducing access time.
It really depends on how much disk access you need to do. I'm writing some mods for a game, and found that when I started compiling on the RAM disk the compile times dropped significantly.