The launch of the voice recognition Siri app for Apple's iPhone a few months ago was seen as a big step in local search. According to ClickZ, Siri's widespread adoption and ability to pull local business information on the go from various data sources made it something that all smaller companies needed to become familiar with.
Many times, because of a smartphone's smaller screen and the fact that mobile searchers are typically on the go, being listed in the top three spots on Google's search engine results page for mobile is far more important than it is on a desktop.
Also, Formic Media notes that Siri weighs Yelp reviews quite heavily when searching for local businesses, and is unlikely to pull results for one or two-star rated locations.
ClickZ conducted an experiment to see how the addition of a four-star review to an unnamed client in Troy, Michigan, affected its positioning in Siri searches. Researchers found that three weeks after placing the faux-review, the client was positioned in the No. 1 spot, despite the fact that it was unlisted when the same voice-command search was previously conducted.