It’s uncertain at the moment what impact this will have on user behavior or traffic to local business sites. I’d love to hear an SEO perspective; I’m sure this is a welcome development.
Based on a call a little while ago with Google, I appended my SEL post:
Google said today that the reason it’s showing more links is because usability testing revealed that many people didn’t realize there was additional local content available beyond the three listings, despite the “more results . . .” prompt. Accordingly, Google said that with the 10 links it is hoping to signal people that there is much more local content a click away.
The ranking of those ten results is based on a range of factors, including the query, proximity, availability of ratings/reviews and their quality and several other variables.
Google also said that it wouldn’t always show 10 results; it might still show three sometimes or one if the query is very specific.