I tried it before, it needs to wait quite a long time for the readyboost to work after you plugged your pendrive. Hard drive light will blink rapidly after you start the readyboost and you need to wait it back to normal then it will start the real boost.
The more size you set, the longer you have to wait.

And ya, 2GB ram can only feels a little, almost like none. But better if you get more RAM coz readyboost is like for low RAM use only....
once you got more ram like 4GB, then you'll feel that readyboost hinder the system performance.

That is what i experinced.