Whenever I finish an audio book, I spend a few days listening to music on my commute instead. The various "favorites" playlists on my iPod are very heavily weighted towards things I like to sing along with, so it also tends to be a very singing sort of time as well.
I noticed this last time around that in addition to matching notes as I sing along (still not always a guarantee) it's also fun to try to match voices. I find myself changing timbre, enunciation, etc., depending on whether I'm singing along with John Linnell, or Andy M. Stewart, or Weird Al Yankovic, or Sebastian the Crab, or anyone else. And then there are songs that switch it all up in the middle, like Swingerhead's "Trying to Cut Back," which has about six or so distinct personalities singing the different verses, each with the singer doing a different voice. Or Robin Williams singing "Never Had a Friend Like Me," with all his silly genie voices. It's fun trying to keep up with it all.
Anyway, just thought I'd share that.