I have had a 4 Gb Buffalo key for some time and was very happy with it, but for one thing; it worked on XP but didn't work on Vista (it couldn't install drivers), and Buffalo ignored my request for help.
When I saw this, and it claimed ReadyBoost compatible, I was very keen to get it, especially given the huge capacity. It has not disappointed me. Works perfectly with Vista or XP and does indeed work as a ReadyBoost source. Doesn't seem to be too difficult to fit in USB slots, although very closely-spaced slots might present a problem as it is slightly chunky. Seems very robust.