Does a "readyboost" USB traveldrive really add RAM under Vista?

Does anyone know if the performance is really enhanced? I have a fairly fast computer: ASUS AN8e MB with an AMD Opteron 170, 2 gigs of ram, a raptor harddrive and a GeForce 7900GS(256megs) video card. I've heard that these external thumbdrive devices supposedly act like more system ram under Vista OS. The ad in this morning's Office Depot flyer says it does. They advertise a 2gig Memorex ReadyBoost Travel drive, and I'm tempted to get it. I know that most will say that 2 gigs is enough ram. I did notice an increase in speed-not measured, just seemed like it- when I went from 1 to 2 gigs in system ram. I have a store credit at Office Depot and want to use it before it expires or I forget I have it.
Anyone with experience in this? Any opinions? Thanks.