Yeah I believe they're used quite extensively. The Robo Challenge mounts are a great low-cost and ready-made solution for fitting drill motors into a robot.
I've used motor mounts in the past but now I just sort out the mounting of them myself. This basically involves cutting the gearbox shape (which is like a pair of 'D's back to back) into whatever material I'm using for my chassis and securing it in place with a mounting plate that comes as part of a cordless drill (it screws in in between the chuck and the spring that controls the clutch action). It's not too complex a process but for a first-time build, I would just go for ready-made mounts. Keeps things simple.