Windows 7 should automatically disable Readyboost and superfetch on SSD
's. Build 7100 did on my Mini 9
Readyboost is to compensate for the slow random seek/read speed of conventional drives. It caches frequently used data (programs you use a lot and OS files) so that it be quickly found and pulled from the quick flash drive rather then the slower seeking HDD. When you have less memory the HDD gets used more, thus RB is relied on more. But even on a system with tons of memory RB can help make things a little snappier, though the effect is not dramatic.
I think the Mini 10 is hard limited to 1gb so there's not much he can do there. If it doesn't have an SSD
it can't hurt to give readyboost a try and see if you notice a difference. It should work just fine with an SD card, and most other forms of removable flash storage, as long as the random read and write speeds are quick enough.