I purchased a USB stick at the weekend to speed up my ailing Sony A190.
Unfortunately the ReadyBoost gamble didn't pay off. Windows Vista ReadyBoost requires uniform behaviour of the memory - my transcend jetflash 110 has, apparently, got 128Mb fast memory and the rest I guess not so flash.
The ReadyBoost FAQ can be found here:
A list of devices and their status can be found here: