with my hayes mechs that i used to have on my bike, one finger braking wasn't really an option if i wanted to stop. slowing down, no problem... but stopping, forget about it.
my new hayes hydros though, are a whole other animal. one finger braking is a sinch. i usually have my index fingers on the brake lever... occasionally i'll have my middle fingers on there, but mostly it's the indexes. i only use two fingers when i really want to stop abruptly to pull an endo or something - i think i do that out of instinct or habit more than need though.
as for the front/rear braking issue... i usually use more front than rear when i want to slow down quickly or stop. but on certain occasions when i just want to slow down just a tad, i'd drag my rear (without locking of course) just to bleed off some speed. i usually do this on steep descents or on descents where there's a turn in the trail just at the bottom of the hill.