The idea isn't bad. It's been done before in Japan by mobile phone carriers. If you opted-in to receive the ads they would pop up when you were physically close to the business. It soon got annoying and I turned it off, but it might appeal to some.
However, I doubt many would be using Twitter to find out more about local bushinesses. Maybe Foursquare or Maps, but not necessarily Twitter.
Starting AskTwitter would put them in competition with Google in multiple categories... that would be interesting. Especially if they used Wolfram Alpha as the engine behind it, at least alongside theirs. When you want facts, Wolfram Alpha is a much better choice than Google... It also does nearest restaurant, even responds to "i am hungry" with nearby fast food places.