Save some time installing Vista. 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.
Improve Vista performance with ReadyBoost. 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.
Carry a suite of portable applications. PortableApps.com packages a browser, email client, backup
utility and more configured to work from any USB memory device. The standard suite of applications fills over 260MB of a
flash drive with portable goodness. Relying on special technology, U3 provides portable apps for U3 smart drives.
Run a different operating system. 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.
Save some time installing Visual Studio. I've done this, and I learned one trick: the flash drive
has to have the name "DVD1" for an MSDN installation to complete successfully. See Aaron Stebner's post for more DVD naming schemes.