Aside from the normal late model XJ issues, like the front speakers not working, window lock getting stuck, the rear hatch needing some love to open, and rear dome light issues.
The cylinder head (0331 casting) on the 2000-2001 models is known to crack, some crack the first time they overheat, others last forever, others crack for no apparent reason. Just keep an eye on the oil and coolant levels, if the oil looks like chocolate milkshake or latte then the head is toast, along with most of the bearings surfaces in the engine. Coolant doesn't magicaly disappear, if a large amount is missing after a fairly short time, its going some where its not supposed to go, most likely the ground or into the oil or cylinders. If the head issues bother you there are a few companies that offer a 0331 TUPY head, which is the improved fixed-the-cracking-issue cylinder head, if you're willing to pay up for the new head and install it.
Also you'll have a low pinion d30 front, its not a deal breaker, but the high pinion is better if you plan to off road it. If it has ABS it will also have a d35 rear axle, also not a deal breaker, but it will be and issue when you try to run larger tires and take it off road. If its doesn't have ABS it could have either the d35 or the Chrysler 8.25 axle, the 8.25 is the more desirable axle. When you look at it the 8.25 has a flat lip, about 5in long, on the bottom of the differential housing, the D35 has a rounded housing bottom.
8.25 looks like this
The D35 looks like this
The one you're looking at also has the NP242 transfer case, its weaker (not by very much, people swap 231>242 and 242>231 all the time) than the NP231 case, the NP231 case also doesn't have the full time 4wd option like the NP242 has, which is nice on icy roads. However aftermarket support (SYE tail housings, 4:1 low ranges) for the NP242 are non-existent.