I'm using a 16GB USB Flash Drive for Ready boost in Windows7 Pro.
Why?
Do you already have 4gig Ram?
Is the card superdooper fast, like 0.20ms access time?
Most flash sticks will give you read/write speeds, but these are averages. This means that one part of the stick might be higher, and another lower ... many 'high speed' sticks actually have one segment of lightning fast memory, and the rest is slow. Another problem, is, these are sustained speeds ... readyboost requires much smaller read/write access ... which means that a device that responds in 1.2 ms, and then reads at 300 MB/s simply will not work ... no matter how fast its listed read speed is.
Hey, I'm not trying to ruin every ones parade here, but I think this myth that 'readyboost' is a numerical 'go-faster-stripe' is a oxymoron ... if you got a 'shop bought' entry lvl laptop, then I'm sure, as they traditionally use slow HDs, you will
see an improvement.
Much of the confusion as to how well readyboost works seems to be because there hasn't been any credible source doing any reliable benchmarks using well spec'd flash cards.
Once you get into the realm of 4GB, there is really no advantage to ready boost at all, and it can, in fact, slow down your system. This isn't me ****ing on your parade, this is Microsoft's word on it.