i have played with the Ipo drivers, and they are very interesting, but I have been disappointed by one thing:
I had the hope that they could solve a problem encountered with Constraints, but the problem is the same With Ipo drivers.
Here is the problem: when you have an object animated by an Ipo, a cube for example, you can copy its rotation on an other object using a Copy rotation constraint. But if you make a third object, you can’t copy te rotation of the second object using a constraint!
The copy works only one time, on the first animated object.
It is the same with Ipo drivers. If you want to use as an Ipo driver an object animated by a constraint, it doesn’t work!