I have the minoura (fork-mounted bracket) I ordered from Harris cyclery, so I can at least give you my take on it: It works great and is very secure -- but a bit hard to feed the metal strap into the buckle to initially set it up. I run a cheap 2 AA flashlight with rechargable batteries for dark mornings, and soon to be dark evenings.

The light is attached to the minoura mount via the two-fish blocks:

http://www.twofish.biz/bike.html

All in all it works great. I've got one on my Surly and my wife's bianchi.