I drove my buddy's E90 with lowering springs. Did not like how the car behaved when it hit the bump stops (which was quite frequently). Made the car feel squirely.
However Dinan offers re-calibrated bump stops with its lowering springs. They are supposed to keep the same travel despite the reduced ride height. It looks like an interesting option.
For reference (Under suspension travel):
http://www.dinancars.com/university/