Yeah, done B mode before, but you still need to limit the exposure before you get too much noise. And since I have to use the camera's noise reduction mode which takes an equal length dark frame and automatically subtracts it (I can't manually take my own dark frames every half hour as you do in astronomy, because the chip isn't cooled and its characteristics change too rapidly), I just always found the lightning would wait until the moment the shutter had closed before going off.
These have been my successes: http://www.flickr.com/photos/spacelama/tags/lightning
(the 4th one, despite landing behind the mountains about 15km away, was absolutely blinding (a good fraction of daylight, given that the exposure is effectively fractions of a second and the mountains were lit up in the photo. If I could have predicted the necessary f-ratio before to stop it down a substantial fraction, it would have been a brilliant, pardon the pun, shot; ooh, wouldn't it be nice to be able to do HDR with lightning)
Now it just makes you insanely mad when trying to do the same thing to capture meteors, which are 100 times rarer during the peak of a shower (which only happens a handful of times per year), and the damn meteor always terminates a degree outside of the field of view, no matter where you're pointing the camera.