Dang, I wish this was the den. This thread could get interesting. 
I can't comment on the front, but I run retainers top and bottom on the rear coils. The upper retainer is a simple bolt through the tower with a spacer on each side. It's set so the coil can unseat about 2" before it catches.
I like them retained because of the little bit of unsprung weight. Feels like more of a controlled droop. I've been running the same coils in back since early '99 and haven't had a problem with the spings. Personally I think a XJ coil would have to be stretched out a long way to fatigue them enough to have problems. I have bent a few from over compression though.

I can't comment on the front, but I run retainers top and bottom on the rear coils. The upper retainer is a simple bolt through the tower with a spacer on each side. It's set so the coil can unseat about 2" before it catches.
I like them retained because of the little bit of unsprung weight. Feels like more of a controlled droop. I've been running the same coils in back since early '99 and haven't had a problem with the spings. Personally I think a XJ coil would have to be stretched out a long way to fatigue them enough to have problems. I have bent a few from over compression though.