Yesterday, so this doesn't seem like an April Fools prank, Google posted in their features updates page for Google My Business that they've updated their help document on local rankings. It says "Learn how to improve your local search ranking with new guidance from Google."
When you go to the document, you can see Google has tripled the amount of content on that page. They also revamped almost all the existing content on the page.
Here is one thing I pulled out that looks interesting:
Prominence is also based on information that Google has about a business from across the web (like links, articles, and directories). Google review count and score are factored into local search ranking: more reviews and positive ratings will probably improve a business's local ranking. Your position in web results is also a factor, so SEO best practices also apply to local search optimization.
Google uses links, articles and directories - yep, it says so. Google uses SEO best practices for local search rankings as well.
Here is the old content, click to enlarge:
Here is the new content, click to enlarge:
I recommend you all read through it in detail.
Forum discussion at Google+.