I am in the process of installing TJ flares on my XJ. So far, so good. They look kinda funny from the front but they're growing on me. I had to cut ALOT of sheet metal.
The first time I tried to just trace the flare by holding it up to the fender. Doing that around all the other stuff I had going on took me 2 afternoons of head scratching, cutting, fitting, cutting, grinding, figuring etc. The driver's side I made a template out of cardboard, taped, traced and cut. Fit right in there, had it installed and bolted up in 20 minutes.
The rear presented a couple different problems, the main one being that I had to cut the outer half of the wheel well out. After scratching my head for a couple hours I decided to just rebuild the whole wheel well tub. Screwed it in, sealed it up and stuffed it full of insulation. Works good, looks even better.
I will post up some pics of the procedure.