I modified the car mount a couple of months back using a cordless drill and different sized bits, going from small to big. I tried looking at other hacked mounts, but it was a little difficult guessing where exactly to place the center of the hole (why camera hole looks crappy). I will eventually fix the camera hole. It doesn't really bother me because it works fine. Originally I was going to try and make the speaker holes into a slit, but it turned out to be more work.
It's been about 5 months since I've modded the car mount (bought in Dec. for 30 bucks & came with car charger) and I am extremely happy with the outcome. I can't say that the motorola car mount is the best because I have not used or seen other mounts. Having said that, the mount is both easy to mod and made specifically for the Droid.
Side note: use the qik app to stream your drives. Seeing the road on the phone makes you feel like you are watching those police chase videos from the dash mounted cameras. very cool.
Droid car mount - a set on Flickr