This is something that surely should be categorized under "Cool". I am using Vista from its internal rollout, far before it was released outside, still somehow I ignored [I hate that person who said ignorance is a bliss] this superb feature.
Yesterday when I was visiting a nice blog whose author [Gary Russo] happens to be my customer, I saw this post. Hey Gary ! great post !
Obviously as anybody else on this planet, I got curious to know more about it, and again immediate help was offered by Gary as a link to Tom's blog titled ReadyBoost Q&A
Wow..! cool.. but unfortunately I was not able to use this feature as vista says that my 4 GB USB drive is not good enough :(