Okay, so there are additional resources taken up obviously, but not that much. Here are two screencaps. The first without Zune running (but with other stuff running) and the second with Zune running.
Sorry for the size, but you couldn't see the gadget without it being large. So without Zune running it was 46% of RAM and with it running it was 49% of RAM. I've got 2GB of RAM so it is using about 40GB of RAM, but that is while being used. When it was minimized it was only at 48% (or 20GB). I wonder how much iTunes uses now.