I recently bought a demo unit (XP-30) with full warranty and with a great price. It's not the most intuitive instrument, but quite powerful when we are familiar with it. If I'm not mistaken, this was the last of the XP series, so it benefits from a superior quality 24 bit DAC, as opposed to 16 bit DACs of other XPs. Not all sounds are usable or useful, but it has one of the most impressive pallette of sounds in a synth (something like 1700 patches), with 3 expansion cards built in from factory. It has some weaknesses in basic sounds like piano, rhodes and organs. Maybe they can be compensated by the use of expansion cards, but I'm almost sure these cannot match the quality of more recent generations of samples. One great feature is a smartmedia slot to store one's own patches/performances, but unfortunately it uses very rare 2Mb and 4Mb 5V cards. However they can be found on ebay.

-- José.