Microsoft Vista ReadyBoost
From a Paul Thurrott SuperSite post:
It sounded like science fiction the first time I heard about it: Windows Vista includes a feature called ReadyBoost that lets you use a USB 2.0-based flash memory device–typically a USB memory key–to speed up the performance of virtually any Vista PC.
This is pretty amazing. Take a flash drive, plug in into a USB port, and expand the available memory (that’s RAM, not storage) without having to open up your PC.
It also looks like Vista will ship in the coming months. Finally.