Considering the iPhone does not have video out, and has space that is woefully inadequate for my media needs, yes I do.
Besides, I feel as though the on-the-go playlist creation and the handling of music is much more intuitive on the iPod. The iPhone is cool and all, but I know exactly where to press to play the next song or change the volume without even looking on the iPod. No unlock button, finger slide, etc, etc.
That said, I usually find myself using the iPod in the car more than before; I usually use the iPhone for walks, or areas outside the car. I get a little worried about extensively playing media when my phone is at about 25% battery life because I want to be able to receive calls.