DiscoStu - Please forgive hasty answer in advance, just to introduce some basics.
There are several aspects to local results. Among these... not necessarily all... one is optimizing your site for organic searches that include geo terms... and another is optimizing for Google Local and Google Maps.
Here's a thread where I'd posted about onpage targeting and optimization for plain vanilla organic search with placename modifiers....
Any Wordtracker Experts Here?
Here's a thread which covers a lot of ground, where we discussed optimization specifically for Google Local....
How To Get My Business To Show Up As A Map In Google SERPs
It's conceivable that Geo Sitemaps might interact with both of the above, but I suspect the data in Geo Sitemaps is more related to Google Earth type searches than to straight Google search type issues. I think you're asking about Google search.
[edited by: Robert_Charlton at 5:19 am (utc) on Nov. 3, 2008]