Some more info from an engineer who worked on the XOOM. (Link)
"I am the engineer who designed the hardware for USB on the Xoom. I can confirm that the hardware is capable of supporting any USB 2.0 (or earlier) device using the host mode adapter cable. The software will, however, have limitations. The software that will be shipping on the Xoom will only have support for USB keyboards. I cannot guarantee this, but I have been told that support for camera connection will be available at some point. This should enable the Xoom to also detect some phones as digital cameras. As far as flash drives and external hard drives are concerned, I don't know whether or not they will be supported.
For those of you looking to buy the adapter, please do not buy a standard micro-USB to USB adapter. It is not going to enable host mode on the Xoom. The adapter sold by Motorola has the ID pin set to host mode, and the generic adapters you can buy online will not."
I'm confident that the great minds at XDA will have this exploited before Monday.