Displaying timezones in the browser for your users

I've had on a few occasion the responsibility to handle timezone in softwares and web interfaces, including fixing complicated bugs related to timezones.

The general direction is to detect the user's timezone via javascript and convert the date&time to this timezone.

If you are rendering on server-side, it is more complex because you must acquire the timezone from the browser and send it back to the server, for example via cookies.