I bought the diesel Liberty because I wanted a 4WD. I like the styling of the 2006 Liberty (no, I know it's not a Wrangler or CJ for those who don't like KJ's ;-) and my Fiance loves it too. So I get a neat little 4WD that will suffice for 95% of my off-road needs unless I take up rock-crawling for a hobby.
I am getting pretty decent mileage with the diesel, 20-21mpg (11.5-12 l/100km) around town, 25 mpg (9.4 l/100km) on the interstate at about 75mph. I figure that's pretty good for a 4000lb SUV with not-the-best aerodynamics, and seems a lot better than the 3.7 gas. I haven't towed with it yet or gone seriously off-road yet, so will update this review once I get some more experience with it.
The seats are a bit hard, but overall OK (seats 5 normal sized folk OK - 4 comfortably), not as comfortable as my Mustang GT was, but then again the Mustang was not really set up to go off-road or tow my boat... suspension is a bit stiff, but it is a Jeep 4WD, not a car-based SUV.
It has plenty of torque with the diesel, which is a great engine, and keeps up just fine with traffic, accelerating at a decent rate. With diesel running around $2.80/gal right now and gas at about $3.15/gal that is an extra bonus as far as running cost.
It's fun to drive, has a great turning circle making it quite maneuverable in parking lots. Also has good visibility and handles well for what it is, a compact 4WD. Jumps curbs well too!