I don’t recall seeing this before, but I stumbled across this quite by chance this morning after upgrading to Chrome 7 yesterday. It seems Chrome is now showing auto previews of sites and searches in the main window, as you type them into the address/search bar.
Starting at Google.com, I began typing in the address of my blog into the search bar. Note, this is without hitting return/enter:
The same happens when searching for a term, and note, the search results autoupdate as you type: