Google Apps aka Google Postini is a spam blocking service that works rather well if you can ever get it configured on your server. Thanks, Google for buying Postini (notice how I just assume Google purchased this company instead of developed it in-house at Google Labs).
All SEO practitioners know that Google prefers algorithmic solutions over manual pulls. Well, it looks like that practice has carried through to their spam blocking email software, Postini, which thinks that the Google Places email carries all the hallmarks of spam. Of course, there is one possibility worth considering. What is this is actually not from Google and someone is spoofing Google?