For my Driver and Angel in an Ambulance game, music plays a big part, because there's a person in game broadcasting music on Channel 9 of the CB radio, and they tune into it while driving. It's a lot of classic rock, and fits the "road trip" vibe of the game we're playing.
I use one of the music channels that the cable provider gives us, which allows for a massive variety. It's hit and miss, sometimes the music is a little inappropriate during a combat or tense situation, but I kind of like that, as we've decided that the music playing is the music coming out of the CB radio, and they can't quite control it.
I find myself incredibly busy as an MC during the game, and adding DJ to the mix would be a lot to juggle. I tend to just let that cable channel do the work for me.
For my other groups, I don't play music with Gamma Road as I'm recording those sessions, and music would ruin any chance of recording.
My other game "The Works" has a few people who get very distracted with background noise, (their hearing tends to get wonky with music in the background) so no music there either.