On the Vancouver Web Consultants blog there's this new tutorial about grabbing latitude and longitude information for a location and determining its current time zone from there.
I was recently tasked with building an application that relied heavily on accurate time zone conversions. I, like many people I soon found out, thought there were just a handful of timezones and the usual select list would suffice. The deeper I looked into the problem, the deeper it got: the list above only shows a few time offsets from UTC, but it doesn't tell me, beyond a shadow of a doubt, exactly what time it is where the user is situated, nor can I rely on that time for calculations in the future. The fact is, here are a LOT of timezones in the world.