If you do local SEO or Google Places consulting, then you know David Mihm's Local Search Ranking Factors is considered THE industry resource. The 2011 edition just went live.
This year the survey focused exclusively on Google Places and excluded Bing and Yahoo. In this time of chaotic Google Places algo changes, you will want to be sure to read every word, especially comments from all the leading local experts.
There is a TON of valuable info, more so that usual, due to the fact that double local algos are currently in play. So set aside some time this weekend to try to get through it.
(FYI mods, I'm never sure which authority sources a link out is permitted to here, so if it's appropriate to add a link to the source, please do so.)