Ironically, neither Google Maps nor Google Mail (GMail) used AJAX/XMLHTTPRequest in their first version. The first Google product that used AJAX came later, it was Google Instant Search (search box improvement). Google Maps and GMAIL used hidden iframes to load data in the background. Around 2004/5 only Internet Explorer 5+ and very recent Mozilla builds supported XMLHTTPRequest (without bugs). As far as I remember Maps and GMail switched to AJAX approach around 2006.