I had a lot of top spots on Places last year but got caught is October 10 for a kword in title violation and my account banned. Started again in February 11 with another account and rebuilt everything from scratch. It came back but no where near as strongly or for the same keywords.
Places keep changing the algo they have done this twice already in the last 6 - 7 Months. Mike Blumenthal and other experts on the subject are convinced G intends to moneytize (similar to an adwords model) the Places service as soon as they get it tweaked to the way they want it, and why wouldn't they? Are they in this game to make money?