[7rojo7]

AB = cymbal mics, like the cdog explanation, there's a vry good explaination on John Sayers site about drum micing and finding the center with diagrams. google SAE John Sayers.
The snare is usually off to one side of the kik (lefty or righty) in a 2 wing tom set the 2nd tom is the one you want in the middle, with an xy setup you wouldn't position the mics as the drummer is faced but on a 30° or so angle to line up the kik, snare and second tom so that becomes your center axis. On 1 tom sets the ride cymbal is usually where the second tom is (in the center). With an xy overheads I use the headphones in stereo to position the drum panning carefully with the overheads. I monitor in mono 90% of the time when I'm tracking.
AB is useful in front of the kit if you have a good room and a good drummer, Over the kit it's useful to get the cymbals isolated, this works for bashers (keep em down) or wimpy drummers (turn em up), but I wouldn't look for any "stereo image" or that's how the drum set sounds (better sound good!) AB works good for Pop where you want to isolate and control the sounds or any kind of speed, death, thrash etc... for the latter you might find your self using ABCD...
I use 3 M260s in an OCT over the kit for a natural sound or the sam mics on seperate stands pointing at the cymbals from the inside towards the outside of the kit to isolate the cymbals from the drums as much as possible.
good drummers and well tuned kits win out over any recording technique.