Adjusting Time Displays For User's Local Time

I have a news/comment site where stories and comments are accompanied by the date they were posted. Currently I'm doing that in the GMT format, simply because it's easiest.

What I'd like to do, however, is have the page display posts and comments with "your time," i.e., the local time of the user (example of what I'm talking about here).

I know how to get local time variables from a user with javascript, but I'm not sure how to pass that information to PHP, especially since I'd like to do this on the front page, which means no passing javascript information via query strings.