I got mine last December, and ran it twice a day, 5 days/week until late April. Mine has the Li-ion battery, so it was a little more expensive. The coldest temperature it was used in was ~-25C + windchill. I had it fail on me once, just before I left for work, but I turned it off, checked the connections and then it was fine. I made my own helmet mount as well:

The helmet mount is made from an old Oakley goggle lens and weighs less than an ounce including the straps and velcro. It is quite stable, especially since the Trailtech light casing is made from metal and is fairly heavy [read: overbuilt for cycling, great for MX]. I don't really notice it anymore, but it takes a couple of days to get used to it. I have the 12-degree flood, and it is very effective. On my commute, it's important to see and be seen, and drivers are not expecting to see a biker riding through the snow when it's -20 out. I don't ever shine it directly at a vehicle unless they stray into my lane or look like they won't be giving me the right of way. Most vehicles give me a wide berth, which is how I like it.

I loaned it to a friend of mine for an adventure race, and it lasted twice as long as any of the other lights, with about 3x the brightness.

The main downfalls of this light are the weight of the light unit itself and the lack of a good helmet mount. The weight is something I can get used to, and the helmet mount is easy to create out of some plastic and a couple of straps. The beam pattern is great, the brightness is unbelievable.