I came close to buying one a couple of times. You can find them pretty cheap but neglected ones are like neglected 911s, open your wallet and start crying. Plus like most British cars you have to do some reengineering to fix the "character" the factory left with the car. Gas mileage is about the same as a truck. Having said all that I still lust for one.
Here's the link to the XJ-S bible:
http://www.jag-lovers.org/xj-s/book/