I had them on a Golf Mark 5, and they were absolutely fantastic - the amount of light they gave off was rather impressive. Unfortunately, it meant that most days I got flashed by people who thought I was being stupid and driving with full beams on. (And, yes, occasionally I got the temptation to flash them back.)
I've got a Mini at the moment, which also has Xenons (a Phillips unit, I think), and I've driven another Mini without them. The normal ones are particularly weedy; the Xenons aren't as good as a Golf, but there is a definite difference. I wouldn't have a car without them now.
Oh, and the washers are quite neat, if you like that sort of thing. I can see the washers squirt the lights from the driver's seat.