Colin, if its any consolation, my S2 did the exact same last week when I was discovering the head gasket is kaput.
As I was in the midst of indulging in the joy that is 2.1 thermostat removal, I stood up for a moment as my back was killing me, and noticed the rear window open a very slight amount (just a wee crack, not even below the seal). Stupidly, I touched the glass, and imagine my delight, if you will, as it just slowly and silently slid down into the door, completely unaided, it wasn't for coming back. Of course just at the precise moment it reached the fully open position, I felt the first droplets of rain on my neck, and saw it start to hit the car. The realisation was compounded as I, with my oil and antifreeze covered, bleeding fingers, slammed the key into the ignition in disgust, pressed the window up button, and heard the completely expected graunching sound of the motor trying to wind a snapped cable.
I must say I did get a few funny looks from the neighbours as I stood there yelling "What now?? What the hell is this?!! You better be f***ing kidding me!!!!", and threatening to put a match to it.
But sure, these things happen don't they. I secured mine in the short term by sticking a wooden baton under the glass and putting a screw into it through a hole in the middle metal arm of the mechanism, it'll do until the head is done.
I wouldn't give them up, but christ them XMs are annoying sometimes aren't they
Ciarán
As it was sunny and a little warm in the cabin I thought I'd exersise all the windows and the sunroof - fine no worries... until I wanted to close them all again - yes, you've guessed it, one of the rear window mechanisms has gone kapput and the window is now hiding somewhere inside the door frame, Oh Joy... 
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, Mike's belt woes, the list goes on, Sympathy Party now seating in room 3? 
