I found out by accident that its not just Chrome that has the combined search and address bar (Omnibox) feature - the address bar in IE8, Firefox 3.0 & Opera 9.6 (the version numbers are the ones I've tested on) can also double up as a search box. You can type your search term in the address bar of any of these browsers and press the Enter key to see results from your default search engine. This doesn't work in Safari (version 4.0 on Windows) though.
Its good to see browser features getting consistent across the board.
Also see:
Keyboard shortcuts common to Firefox & IE8
View math calculation results directly in Firefox Search bar