Windows Vista ReadyBoost
In case you didn't already know, Vista makes use of this feature called "ReadyBoost" where you can use a standard USB stick memory, or Memory card to augment your system's performance. Not all memory is compatible and must meet some performance specs which Vista tests for you upon insertion. Also many USB sticks now state whether they are ReadyBoost compliant.
ReadyBoost Tab in Properties of USB stick or other flash memory card.
I've used it on my home system for about a good month now and I do notice a significant improvement in overall performance. It's like I added more RAM to my system without opening the case. Like most everywhere else, it's hard to substantiate in numbers the difference. I do wholeheartedly suggest trying it for yourself. I mean when you can buy a 8GB USB Stick from $12 - $25, it's kind of hard not to try it.
You can find out the details of ReadyBoost here: