Everything T-Dawg said is true 07's definately have had their issues, trust me I have 2 of them. This was the first 800r motor released by ski-doo, albeit powerful, being the first adopter means discovering the issues. Crank problems as I have come to understand, were focused around a case production run, that the tolerances of the crank case being too tight on the inner bearing causing them to cold seize. Rule of thumb is, if you have over 2000 miles on your crank or got a rebuilt motor from skidoo with the R punched by the engine support, you were in the clear. BJ can also line bore the case for about $200 shipped.
The clutches do wear and need maintenance, when replacing the spring cap, you should replace with the 08 version (or the one that comes in the box) as it has the same part number as the 07 (or the one that comes in the bag).
If you are seriously considering the 07, someone will eventually poke you in the eye and say read this...
http://www.mxzx-revzone.com/article/2007-summit-xrs-138.asp#clutches
There is a lot of good info on that link that I have found to be true.
On the flip side the XP's have their issues as well, retarded timing curves, knock sensor issues, broken driveshafts, and lets not forget the front end. If you do any mountain riding and loose the sled into a tree, on the rev you may be looking at replacing a $200 nun, on the XP you maybe calling your insurance company and replacing the entire bulkhead and tunnel.
I am on my 3rd tunnel on my sled, however, my wife seems to miss the trees and is still on the original, I just don't think she is trying...
