I've done it and it's been fantastic. I put a giant Lincoln Mark VIII fan inside of the stock fan shroud and controlled it with a Flex-A-Lite variable controller. It hasn't given me any problems and I like that it turns on the fan at 60% when the AC is running and has the ability to turn it on or off via switches. It also has a soft start feature so there isn't much risk of blowing fuses.
Now, that being said, I did the electric fan so that I could turn it off for water crossings. If I didn't plan on that, then I would have just stayed stock or upgraded the mechanical fan/clutch with something bigger. There's a thread on another jeep forum about using Ford Explorer and Mustang fan/clutch combos for increased cooling that sounds interesting.