I was wondering the same thing (regarding our Moguls not auto-updating)... recently came across the GPSToday app (see thread at
http://forum.xda-developers.com/showthread.php?t=370384) and just made a post with a feature request that I hope will be in a future release (see
http://forum.xda-developers.com/show...&postcount=158)... basically the idea is that it would take your latest GPS lock, feed it to a server online to return the timezone, and update your visiting time based on that.