Shackle lifts seem to be pretty popular here, which kind of surprises me. Generally they are not a desireable way to lift a Jeep, but they are cheap.
A buddy of mine had a shackle lift on his Jeep, it served the function of allowing him to clear 31" tires on tired stock springs but that was about it. The front ones hit every rock on the trail, and the rears severely limited his departure angle.
One thing to remember is with a 2" longer shackle you only gain 1" of lift. They can also affect your driveline angles, and possibly cause vibrations, and premature U-joint wear/failure.
I would reccommend saving the money spent on the shackles and get a mild spring lift. Two inch spring lift can be installed without really having to change anything else, except maybe shocks and extending brakelines. Brakelines can also be extended by moving the hard line from the top of the frame to the underside of the frame, and using the rear bolt on the bumpstop as a mounting bolt. Extreme care must be used if you move the hardlines, if you kink the lines you're screwed and have to replace them.
91YJ Sahara, SOA, 4.88's, 35's, Locked