Type in all or part of the title, tag or address of a page to see a list of matches from your history and bookmarks[Found via Larry Dignan]
Results are returned according to their frecency (a combination of frequency and recency of visits to that page)... An adaptive learning algorithm further tunes the results to your patterns.
Update: About two months later, Todd Bishop quotes Mozilla's Mike Beltzner as saying:
I confidently predict that the Awesome Bar is going to change the way people navigate the Web.
It's solving a new problem on the Web -- that the Web has gotten so big, and revisitation is more popular than novel navigation. People go back to sites they've been to before much more than they go to new Web sites.
Understanding how to simplify revisitation is a really big thing for the Web. It totally will change the way you browse.