In yet another research note to investors, Gene Munster today said that AppleTVs are going to get updated at September 9th event. His rationale? The 40GB version is taking 1-2 weeks for delivery at the Apple Store (160GB version is next day). He pads this by saying that the AppleTV hasn't been 2 weeks behind in shipping since he's been tracking the device.
He hypothesizes that the 160GB version will stick around and Apple will have a bigger model(s) ready for release next week. That is pretty light evidence, but on the the other hand, AppleTV is LONG overdue for an update.