I've heard it all "What if I buy an EF-S lens and then upgrade to full frame?"
Sell your EF-S, then, and upgrade. Enjoy the upgrade.
Here's a new bone to chew on: What if I upgrade to full frame, then buy a 40D and miss my ultrawide capability for the 40D?
I'm an ex-10-22 owner who had and loved that lens a lot. Thinking that it may be time to welcome my 10-22 back so my 40D can have ultrawide capability. Sure, it duplicates my capabilities, but then I have a choice of either camera body and a full spectrum of coverage from ultrawide to supertele. Really the 10-22 is the only EF-S you need, you can cover everything else using EF lenses if you are really that keen. Plus I'm a serious, SERIOUS ultrawide user. A quick glance at my prints hanging on the wall and filed in my portfolio would testify to how effectively UWA's have been deployed.