Cave_Troll has got quite a fun effect with a long exposure, doing most of the lighting with slaves and minions (like slaves but self-carrying...), but getting a person with their lamp on to walk across the shot and towards the camera, pointing the light towards the camera. It ends up looking like a UFO flew through the cave.....
I have a Canon poweshot A75 and have mnaged some very good underground shots. I have used flashguns fired manually, only limited by the maximum shutter opening time of 15 secs and the fact my flashguns are old and charge slowly. I also got some good photos of stal curtains lit from behind with a halogen caving lamp, which was very atmospheric, and minimsed light spill.
Tried "painting" today in a couple of u/g locations.Didn't use a flash,I used one of those cheapo zillion candlepower lamps instead.
I'm very impressed with the results indeed.