I've been asked about the Archdiocese of St. Louis's online parish search mapping functionality enough times that I finally made a quick video walkthrough of how it was done. The video below explains it all—basically, we use the Location module to attach addresses to nodes and geocode (get lat/lon) the addresses, and we use Views + Mapstraction to make the spiffy maps all over the site.
The functionality was originally set up by the kind folks at Palantir, and tweaked a bit over time by me to make what you see today.
You can watch the video in HD on Vimeo, to see fine details. (Recorded with iShowU HD).