I didn't bother with putting any on when I installed the lift but, I finally got sick of the back tires rubbing on the fender flares any time they stuffed (and a wheeling buddy pointed out the 1/16" gap between my shock mount and the inside of my rim on the fully drooped side) so I cut a couple of poly spacers from some extra stuff we had at work (stole it from the molding dept upstairs

). I finally got around to putting in an extra upper iso on the rear last Sunday so I figured it was a good time to extend the bumpstops as well. Now, the wheels only come about 1/4" from the shock mounts at full droop and I can get my fingers between the tire and the fender at full stuff.
I may not have NEEDED to extend them but at least I don't have to worry about tearing anything off, now. Never had a problem with the front so I only have the stock bumpstops there. If I ever notice any odd contact, I'll have no problem making a set of longer ones for it, though.