If you’ve got a Mac with multiple CD/DVD burners—a Mac Pro with two installed drives, or any other Mac with a combination of internal and external drives—you can burn two (or more, perhaps) CDs at a time in iTunes. This assumes, of course, that iTunes sees both of your drives as units with burning capabilities. You can check this by going to the Burning tab in the Advanced section of iTunes’ preferences—if you have more than one usable burner, the CD Burner entry will show a pop-up menu that allows you to choose between the units.
Unfortunately, there’s no way to specify which burner you want to use when burning a given playlist, so it’s not exactly intuitive how you might burn two at one time. The answer is straightforward, if not obvious. First set up the two playlists you’d like to burn. Insert two blank CD-Rs, and then start your first burn in iTunes.
Now open iTunes Preferences, and return to the Burning tab in the Advanced pane. Click the pop-up next to the CD Burner entry and select your second burner. Close the Preferences screen, and start your second CD burning.
I’ve tested this with two CDs at once, and both burned just fine. I’m not sure if it will work with more than two units, though I don’t see why it wouldn’t.