What he said, and go to dootalk, read up in the MachZ forums - TONS of information.
If you _still_ buy it after reading all the horror stories (and there are plenty...), take care of the handful of things that need attended to & away you go.
I bought an 05 1000/162 this summer, I've put roughly 500 miles on it this season (total of 1500), I like it a whole lot in soft snow.
It sucks on hard snow; the weight is very, very noticable. Soft snow, the thing is magic. I don't regret buying mine, although reading about all the problems people have had scared the heck out of me.
IMHO, filtration of some sort (I put screens on the horns in the airbox) is a big one. A lot of people put filters on them. I relocated my fuel pump, cleaned all the electrical connections, new O-rings on the injectors, 15w chain, did some clutching, shrug, it is a pretty awesome sled.
I agree with the above poster, though - $3900 seems like a lot; or, maybe more appropriately, if I had $4k to spend on a sled, I'd probably be looking for a Rev 800 - I have about $2k in mine, total. That said, I've really grown to like it, ehhh, who knows. I use mine for skiing - it is a pretty freaking astounding sled for moving two people up (any) hill, fast. I'm kinda looking for another one now, but hoping to find one that needs a fuel pump/motor/whatever.
.02c!