using the API's geocode search, I can give a geolocation and i recieve results... works great
however its not a complete list... for example, most iphone 3g users who post using iphone show up.. in a geocode search, probably because the iphone provides their lat/long coordinates... Users who post over the web using a comptuer are not included in this geocode result.. does twitter/api NOT reverse geocode users ipaddresses to get an approx location so that they can be included in a geocode query?
