Here is the story on the Fusion Model. In 05 and 06 Polaris went to the "up" riding position to follow suit with the other big boys. They rolled out the Fusion 600, 700, and 900. The problems with the 900 motor was a huge problem for the Fusion line. It was such a huge problem and so widespread, it drew acclaim from the 600 and 700's. Basically, the 600's were great sleds that had a few minor recalls, LIKE ALL SLEDS DO REGARDLESS OF MANUFACTURER. These 900 issues caused Polaris to discontinue the Fusion line, and go to the IQ line.
Now the cool part has arose. The bad press on the Fusions, has caused the value of them to take a big hit, but the 600 is still a great sled. I bought a stock 600 with 300 miles on it last year for $4K. Put 1300 miles on it with ABSOLUTELY no problems until I wrapped it around a tree stump in Eagle River in early February. (I then moved to a 08 FST Dragon which was a steal as well.) I was so confident in the 600 Fusion, I found a brand new 06 Fuse 600 (still in the crate) in July at Iron Mountain for under $5k!!! I snatched it up for my girlfriend.
Bottom line is, the 2006 Fusion 600 is a perfectly fine sled, and the prices are great!!! BUY ONE NOW, if you have a chance!