Usability 
Urbanspoon is a crowd sourced guide to dinning out in about 100 major metropolitan areas in the US and Canada. The web based start-up launched a location aware iPhone app shortly after Apple opened up the platform to third party developers. The app quickly became one of the 10 most downloaded apps on iTunes. Urbanspoon really hit it big after Apple featured it in a commercial. In a nice exit for the founders, the self-funded three man start-up was acquired last year by IAC for an unknown price that is generally believed to be several million dollars.
I recently discovered Urbanspoon's mobile website at urbanspoon.com/m. While it has the look and feel of an iPhone web app, page sizes under 100 KB and no JavaScript dependencies mean it will work well with the majority of mobile browsers.
After picking a city, the site lets you search for a restaurant by name or keywords or browse by neighborhood and/or cuisine. Listings feature a percentage ranking based on the number of "Like" votes by users and generally include address, with link to a Google mobile map, phone number, approximate price range, critic reviews from IAC owned CitySearch, blogs and local newspaper critics plus user reviews. Mobile usability could be better, though. Phone numbers are not click to call and their is no information on what days and hours each establishment is open.
Urbanspoon's chief rival is Yelp (Yelp mobile review). Both here in Yelp's home base of San Francisco and in Seattle, where Urbanspoon started, Yelp seems to have slightly more restaurant listings and many more user reviews. I think Urbanspoon's inclusion of critic reviews, which I tend to trust more than user's, makes the two services approximately equal in usefulness for finding a good place to eat. Yelp wins big on usability though by providing by click to call numbers and open hours listings.