Motorola's tablet, rumored to be called Stingray, has showed up in Verizon's inventory with the name MZ600. The tablet is supposedly going to be launched in October. That's about the same time Android 3.0 Gingerbread will be announced, and the Stingray tablet is rumored to have Android Gingerbread on it. It makes sense that Google and Motorola are going to announce it at their Android 3.0 event. After all, Google has teamed up with Motorola before, at Android 2.0 launch.
I wouldn't be surprised if they give each developer that attends the event one of these tablets, the way they gave them an Evo 4G at the Google I/O event, when Android Froyo was launched.