I bought a set of these. One is mounted with two crossed hose clamps onto my commuter. They're brighter than the 1W PB light I also have on that same bike. I use them on high and its pretty decent for 15mph. I'm not sure I'd go a lot faster than that on a dark road, but that's not a serious problem for me -- on the flats at least.

NimH AAAs are good for at least my regular roundtrip commute and I've got a charger at work. With the hose clamps it takes a screwdriver to get the light off, so I just pop out the battery carrier.