I would only ever think about fitting one if I was a proper track *****. No way on earth would I otherwise drill through a body thats been dipped, dunked, coated, and sprayed to prevent corrosion. Long term I dont think a dab of silicon is going to prevent water/moisture penentrating the drilled holes and starting the rust process, especially in a bloody suspension turret.
I'm no expert though, thats just my thoughts on why I wouldnt fit one in my own car.
[EDIT] A game for all our 4 and over members...guess what the auto-edited word is :S