I have two IBPjrs (from Mercenary Audio, actually...) and I have limited experience with them. However, I have been using them a bit since I got them back in January. I've used them on toms, outside kick and snare. They are really great for getting your inside and outside kick mics to hit together the right way. Also, I've used them to get my top snare in phase with the overheads. Once again, it really works like a champ. I just flip the phase and play with it until I get the thinnest sound possible and then flip it back to hear what it sounds like at it's most "in phase" postition. Then of course, I will bypass it to hear what the ultimate difference is. I wouldn't mess with overheads. They're kind of a no brainer if you just go X/Y somewhere in the middle of the kit about four feet or so from the snare. The trick is to get the snare peak from your overheads hitting -5 on your VUs (in mono, or course) and then get the snare mic hitting -5 as well. Put them together and go to town with the IBP. The first record I tracked while using these things came out excellent. The mastering engineer asked the producer that works almost exclusively with me where he tracked the record. I guess it didn't sound like me!
Probably because my drums sounded even bigger than they usually do.