Что делать с большой и быстрой флешкой?

Увеличить быстродействие.
ReadyBoost allows Vista to use a fast USB memory device as an intermediate caching area between memory and disk. Tom Archer has a ReadyBoost Q&A with the technical details.
Сократить время установки. 
Kurt Shintaku describes how to format a bootable flash drive with the contents of the Vista DVD. If your machine can boot from a USB device, this approach does shave some time off the Vista install.
Работать с разными ОС.
Live USBs, like Live CDs, are bootable flash drives with an operating system installed. Wikipedia's list of
LiveDistros contains many Windows, *nix, Apple, and DOS distributions that fit on a key.  >>