I use stakes often. The trick is as has been mentioned is that you put them down in the deployment phase. So you let your archers put them down where you want them and then you move your archers onto a desired location.

Using stakes during seige will stop a cavalry heavy army almost no matter what!!! It almost feels like cheating.

The trick with stakes is knowing where and when to use them, but often they have been the difference between winning and losing in some battles in my english campaign