I picked up this light about a month ago when I learned that the bulb for my Arc light costs $150. L&M "felt my pain" and offered a $150 discount on anything on their site. I also had a gift card, so I went for the good light.
I've taken about 5 dark rides so far, and it's stellar. My basis for comparison is my old Are/LiON unit, which was rated far lower in output than the Seca, but was still a pretty good light. The new unit throws a strong beam that allows me to see (...guesswork here...) about 50 yards, and illuminates the ground close to the bike, as well. There's a second row of LEDs that face down for this, and it's very useful for spotting potholes and debris. Nice touch. Yesterday morning's ride was through a pretty thick fog and the light cut through that very well. No issues.
The unit is simple to work with only two modes; one that cycles through all four settings (high, medium, low, flash) and "race" mode that cycles through high and low. I've used "race" mode most of the time, and use flashing when daylight gets low or I'm riding through deep shadows.
Battery life seems to be as rated, and I'm getting a little over three hours on high. I haven't run it long enough on anything else to drain the battery, but I'm guessing that L&M's ratings are good there, as well. The head attaches using a strap, which works better than you'd think. The battery attaches to the top tube via Velcro, and holds very steady. Charging takes a few hours, but honestly I haven't hung around long enough to provide exact measurements.
Anyway, if you're in the market for a bright light with very good batter life, give this one a look. Not cheap, but worth it if you, like me, refuse to stop riding just because it's dark.
Light and Motion makes great lights. If you're riding with on high though, good luck with that thing. I have the pissed a lot of people off with it before I switched to totally different lights. It's not just bright - it's designed to be a wide spread mountain bike light.
If I was somehow biking somewhere where there was no one else coming, but still had street lights that screwed with my night vision, a combination of a Seca 900 on high and a Seca 1400 on medium was my favorite though.