Okay, important things to know about the Haiku:
1. It runs on either a CR123 or RCR123 battery, and it can handle input voltage in a range of ~2.5V-5V.
2. There are three emitter choices at present: Cree XP-G, which produces a smooth beam with a fairly bright center; Cree XR-E, which "steals" some light from the inner part of the corona to make the center brighter; and Nichia UV, which is only useful if you need a blacklight.
3. The XP-G version is newer and more efficient, so it's slightly brighter than the XR-E version (though the center of the XR-E beam
looks brighter, due to the "stealing" I mentioned before). The XP-G version is also available in cool-white and warm-white. Personally I recommend cool-white, but everyone has a different opinion (and reasons for it) regarding tint.
4. It's made entirely from titanium, which is harder than hell, won't corrode (ever!), and just as easy to polish as it is to scuff. You'll have to hit it with an axe to do more than scuff it.
5. Titanium is bad at conducting heat, as far as metals go anyway, so Don designed the head of the Haiku to include a heatsink that would dissipate heat near the source instead of relying on your hand to keep the light cool. It's very effective, possibly the best thermally-designed titanium flashlight I've ever seen.
6. The heads and battery packs are compatible with Surefire E-series flashlights. You can also unscrew the electronics as a unit and put different ones in as they become available. It's called the Aleph system, which is an obtuse reference to mathematics dealing with infinity, with the obvious implication that you can come up with an infinite number of parts combinations. In real life, the number of combinations is somewhat less than infinite, but they're working on it.
7. The Haiku is not the brightest light you'll ever use, but Don has an unusual talent for designing reflectors that make very usable beams -- the center is bright enough to throw a couple hundred feet, the corona is wide enough so you can see things you're not pointing the light directly at, and the transition between them is very smooth so you're not constantly having to flick the light around to make use of the hotspot.
8. McGizmo pocket clips are among the best you'll ever see; very low-profile and very strong. You can remove them and bend them a bit to get a stronger or looser grip as you desire, but make sure you use a really good 1/16" driver to remove the clip screws, because titanium threads have a tendency to grip like they're welded together and it's fairly common to strip the screw heads with cheap drivers. That being said, you don't HAVE to do anything to the clip to make it work right.
9. Speaking of titanium threads, you'll need special lubrication for the threads that hold the light together. Titanium hates lubrication, and it takes special stuff to stick to the threads and actually do its job instead of getting pushed out of the way so the threads can grind on each other. The most common stuff people use here is called Krytox, which you can find a zillion references to on CPF. I use stuff I made myself called TiTi Twister, but it requires changing the O-rings.
Between the Haiku's utility, durability, and aesthetics, you WILL enjoy using it. On the off-chance you don't, you'll be able to sell it quite easily, unlike cheaper lights. Just ask run4jc, who asked me to talk him into getting one, and then he bought several more.