I have got a 2006 RX Warrior (the european version of Attak) that is used mainly for aggressive trail riding.
My sled is modified using Ohlins shocks (the electronically adjustable shock in the rear), C&A Pro skis, Excell Motorsports exhaust and also some smaller cosmetic changes.
I can not really comment about the performance of the stock sled because most of my modifications have been used since the sled was brand new. Anyway, after installing these modifications and giving the suspension and the weight transfer some setup time, I am very happy about this sled. Right now I would say that, in total, this is probably the quickest and best trail sled I have ever ridden or owned (including couple of modified two stroke Yamahas, an older RX-1 and a modified Ski-Doo REV). It is for sure not as quick as the REV on very tight trails and probably not as compliant in the very big bumps, but as soon as the trail opens up just a little bit it will smoke the REV just by the combination of engine power, suspension function and chassis stability.
I can not really think about any cons except for the quite heavy weight, but if you are planning to buy one I guess you already knew about that. Anyway, the heavy weight seems to be very well balanced, you do not really think about it when riding. The only time you really notice is when you get stuck or when you move it around on the garage floor (that is why you have got reverse, stupid...).
If you are a frequent visitor to this site you are for sure aware about some problems that have been reported. I have never experienced any of these problems (wheels that fall apart, shocks that leak, shock wires that break, tunnels that bend, chaincases that blow, darting, etc.), yet my sled has been ridden very hard. The hand warmers are a little bit on the cold side, but the fix with the plastic washers is working also in Sweden...
Like somone else said about the hyfax wear, they wear quite quick in the beginning but after that initial wear they seem to last for a very long time (in the end I guess no better no worse than any other sled).
Hope this helps,