Scott,
I saw you blog post about Geocoding. I do proximity search on Aging Safely's Listed Homes page. As you can see it is lightning fast. I'd be happy to share the methodology that I am using. The one part that I don't do is capture the IP address and convert it to a default location. My experience in this area is that the available databases are error prone. My location (actually Verizon's central office) is Bothell, WA. Now since Verizon has moved me from ADSL to 5/2 fiber some days I show up in Blthell and other days in Kirkland, WA - someplace on central US, and even Virginia --- Yuk. When doing some work with Lee Sykes of DNN Creative he showed up from London rather then the central UK where he is located.
/DaveS