The following plugin for SocialEngine uses Google Maps for proximity searches, maps, etc.
http://www.socialengine.net/customize/mod-page?mod_id=211&mod=Google-Map–Locations-Plugin
Additional Note: The website will also be using a directory plugin.
Is it necessary to purchase a commercial Google Maps API key for this kind of activity? Somebody suggested that a Google Maps API key was going to cost a lot of money, and for a starter business this wouldn’t be possible.
Plugins do not tend to mention this, but I am led to believe that there may be an issue here.
You can find the information you need in the Google Maps/Google Earth APIs Terms of Service and via the FAQ. Specifically, search the FAQ page for the Q&A “Can I use the Google Maps API on a commercial website?”
Essentially, as long as your site isn’t getting super high traffic, you should be fine with the free level of service.