The new software messages directs users to http://www.tivo.com/expand - but that's still just a placeholder page.
In addition to enabling eSATA support, 9.2 appears to enable progressive downloads for Amazon Unbox, and presumably TiVoCast content. That means you will be able to begin watching the program before the download is complete - similar to an in-house MRV transfer from another TiVo.
These pre-releases generally last a couple of weeks, then, barring any problems being found, the full release comes out for everyone.
I picked this up via ZatzNotFunny.