Update from original reviewer. Yes, I meant water in the fuel ;-)
I ended up trading this Jeep this year (2012) for a truck (Dodge Ram 1500 Outdoorsman, which I love). It had 92,000 miles on it when I traded it. Mileage was still around 21-22 overall, 25+ on the freeway.
I did have an issue that really bugged me. Around 87k the ABS, ESC and traction control light came on. The ABS light would go on and off; the others might, or might not follow suit. I could feel the ABS engaging on dry pavement - pulsing on and off like it was on very slippery ground. Traction control came on occasionally too - on dry pavement. It was a real nuisance, and the dealer said there was nothing wrong when I brought it in. Either they didn't take it for a drive, or it didn't act up for them.
I was not sure if this was a major electronic failure or what. So I did some online digging, and found that this was not uncommon with Liberties. The general consensus was that wiring loom wear and/or the ABS sensors were causing the problem. Given that the sensor was only $14 at my local friendly (but incompetent) dealer, I bought two of them, one for each rear wheel, and replaced them. Took about 15 minutes. Result, the problem was solved completely. Hope this helps somebody else.
Also, if you are considering a used Liberty diesel, be aware that at 100,000 miles you need to replace the timing belt. A really good price for that from a dealer is about $1600 USD. Yep, about four times what is costs for a gas engine. That is pretty typical for the European style diesels that use timing belts (VW for example). And it needs to be done because the valves run interference with the pistons, and a replacement engine is over $10K. Just some free advice, if you are considering one of these, you might want to check on that little bit of maintenance.