If you search, something like [italian restaurant ny], the local search results are more useful than the web results, so Google displays a OneBox that includes these results at the top of the page or in other position. Google has recently increased the number of results displayed in the local OneBox from 3 to 10.
In January 2007, the OneBox was enriched with a static map, information about reviews, directions. To make room for 10 results instead of 3, Google removed the addresses, the links to directions and the ratings.
It's very interesting to see that the other general search engines (Yahoo, Live Search, Ask.com) link to pages from their local search engines, while Google links to the homepage of each business. Another difference is that Google's box has a variable position, depending on the relevance to user's query.
Google, Google Local, OneBox, Search, Web Search, Search Result