Time Machine: local and then over AExtreme?

I recently got an Airport Extreme and we have two macs in the house that we'd like to back up. I realize that 1). the AE port is only usb 2 and 2). wireless transfer is slower than hard wired.

Does anyone have any experience doing an initial Time Machine backup directly over USB followed by ongoing backups where the drive is connected through an Airport Extreme?

I don't believe it would matter, but we'd partition the drive so both macs could back up to it. And, so everyone is comfortable, this would not be our only backup solution just something that's intended to be set and forget.

Thanks for any information,
Keith