I've got the first production kit to hit the US, only problem is there's no snow yet to test it on.

For those of you that are curious, reasons I purchased the kit:
Fuel Economy I get close to 40mpg running the bike in the summer. Say the track takes 10 mpg off of that in the winter...I'm still at 30mpg. That's a third the fuel bill of an average sled. $75 for a day in the snow on a sled or $25 for the day on the bike.
Maintenance My bike is a whole lot easier to work on than a snowmobile. Typically cheaper too.
Power/Handling I'd like to see the sled guys effortlessly lean your snowmobile into a corner on the trail or zip through trees that are the width of your handlebars like you were riding single track in the summer! Sure a snowmobile has more power, but it also weighs a lot more too. A 2009 Yamaha Phazer's dry weight is 515 lbs. My bike with the kit is about 300. That's a lot less weight I have to throw around when I'm in the tight stuff.

Also, according to the Yamaha website, the Phazer is in the 80 HP class, my bike it at about 45 HP. With those numbers the power to weight of the Phazer is around .155 and my bike is around .15 also. So I'm not really loosing anything. This is just a general comparison though, I know there are sleds out there with higher power to weight ratios, and also ones with lower ratios, same goes for bikes. Put the kit on a new WR450 and you have more power, and less weight than my WR400. It's all subjective, but in general, the bike has less power, but it is also much lighter than a snowmobile.
I love my bike I love riding motorcycles, the ergonomics and how they handle. I'm the only guy around this part of the state that is hard core enough to ride his dirt bike all year round. The attached picture is of my tires I ran last winter and would run this year if I hadn't gotten the track.
Can hit the powder My studded tires work great on the packed/semi packed trail as I can run 70 mph with out too much problem, but get in the powder...lets not go there.
Transportability Being a college student still, I'm not in a permanent residence. I can transport my bike a whole lot easier than I can a dirt bike AND snowmobile.
Shiftable transmission Last I new you didn't have different gears to choose from on a snowmobile. You want to go fast, you rev the motor. With my bike if I want to cruise 60 mph, I pop it into 5th gear and cruise along. I also have the option to change gearing depending on the riding I want to do. I want to cruise the trails, I put my 15t sprocket on, I want to play off-trail, I put my 14T on and get more torque. Those two features make the power from my single cylinder 400cc bike very usable. I'd like to see some of the sleds do that!
I'll be able to comment further on the above reasons once I get a chance to put some saddle time in, but that's why I personally chose to get the kit. Take it for what it's worth to you.
I can't say too much about the negatives at this point for performance, I'll be able to tell that once I get some snow. Only cons I've run into so far are a couple design features I really don't like from an engineering stand point (I'm studying to be a mechanical engineer) but I'm working with AD Boivin to see what can be done to satisfy my concerns. I'll report in when I get more info.