Authenticated user should see date/time converted to his timezone

The idea behind date-specific timezones is that the date has a timezone of its own and should be displayed using that timezone. The use case is a site that shows real world events that take place in various timezones. For instance, a concert that starts at 8pm Eastern Standard Time would always be displayed that way because that's what time it will take place for the people who are actually there.

Currently there is no option to show dates in the user's timezone because we don't know reliably what timezone the user is in. We might know their offset, but there are several timezones that could share that offset. I see you came up with an idea of how to do that, but I'm not sure if it will work correctly or not. The best answer is to add a patch to core to track the user's timezone in the user record, and I've proposed a patch to do that at http://drupal.org/node/11077.

My hope is that this will get into core, and then I can add to the Date module a way to properly handle a new option on dates to show them in the user's timezone.

This may not be exactly what you were asking for, but the 5.2 version will have an method to track users' timezones so we can adjust the date properly for the user. It also uses the PHP 5.2 timezone handling which works MUCH better and I hope it will eliminate most of the problems with timezones.

The new version is in HEAD and is not ready to use yet. Wait until I create a 5.2 branch before using it.