is there any possibility to determine the timezone of point (lat/lon) without using webservices? Geonames.org is not stable enough for me to use :( I need this to work in PHP.
Thanks
I had this problem a while back and did exactly what adam suggested:
IIRC it took less than 1 second to populate the R-Tree, and it could then perform thousands of lookups per second (both on a 5 year old PC).