I am using results from a variety of "location-neutral" keyword position trackers like Rank Tracker, SEObook, and of course SEOMoz among others, and comparing them to multiple non-logged in browsers on multiple devices that area actually in the Anytown area. The discrepancies between the various trackers are minor and I would attribute those to datacenter differences.
I considered the personalization possibility, but usually that works in the other direction, unless Google is now using a "you already looked at this enough and we are showing you something else to broaden your horizons" calculation.
I used "500 miles" kind of generically. I tried entering all sort of different locations into the Google settings and it seems the closer I got to Anytown, the lower the ranking went.
I am thinking it is something that recently changed in the way Google handles local search. My theory is that within a certain radius of the specified location, the algorithm is a little different. Once outside of a certain radius, traditional non-localized algorithms kick in so a site optimized for Anytown Widgets might rank a little better than it would when google sees that the searcher is actually in Anytown. I am going to take a closer look at some other local SEO projects and see if anything similar is happening, then see if I can find some common traits.
Not a huge issue as it is a relatively minor drop for some keywords that aren't high volume. But I am a little obsessive and curious. I was hoping someone would chime in with some info about a documented change in Google's local search. I know Places has been evolving a little more lately. Every time I look a my own listing it looks different.
Thanks again.