so we mic'd up a drumset with a marshall cab last night at the studio...

I don't own a camera but I can describe it, it was on the floor on its side- I used a 1936 oversized 2X12. It was about 9 inches to a foot away from the kick with the centre on the speaker roughly in front of the hole, his hole was off to one side so I moved the cab accordingly
 
Like this?
cabmicing.jpg
 
Yeah pretty much!
I didn't spend alot of time on it, just kinda stuck it there and liked what I heard when I listened back to the first positioning I tried. I could be wrong but I'd imagine the placement with something like this is alot less sensitive to position changes due to the sheer size of the "mic" involved.
I'd definately give it a go if you've got the spare channels- it only takes a second to get it up and the low end that it produces is huge. Worst comes to worst you've still got your regular kick mic inside the drum and you can just ignore this in it in the mix. The band I used it on are a pretty old school Doom metal band- kinda like cathedral wit some really slow kinda droning sections so its all about a huge low end, this is perfect for it.