I had a nice long explanation typed out, but it got lost due to some stuff , so here's the short version:
I've got a laptop running Fedora 16, and NetworkManager. It has a wired connection and a wireless connection. ifconfig reports a different ip address for each, as I would expect. When the wired connection is not plugged in, I can ping the laptop on the wireless ip. When the wired connection is plugged in, I can ping the laptop on the wired ip. However, when the wired connection is plugged in, I can't ping the laptop on the wireless ip. WTF?
I can provide more details as needed. Thanks for the help!
Edit: hmmm. After some more research, it seems that this is the intended behavior, and having multiple connections at once can have some nasty side effects in certain circumstances. I guess I'll just work around it. Oh well.