I have a Detroit TrueTrac (no locker FYI) LSD in the Unlimited. It is absolutely fantastic for on-road use - better traction on wet/ice and lays down the power in the dry, especially around turns. I don't think they work well for off-road, but that's not my bag.

I think it's the best performace addition I made, other than my engine of course. BTW - I kept the stock 4.10 ratio but I suppose it all depends on where you want your power.