Date form to unix timestamp
I'm pretty sure the values stored using the date attribute are unaltered and just passed on in an array. So the question would be if the user submits the date for UTC or his/her timezone. I would say the latter ;-)

I'm no expert on date settings and timezones, but had seen this question before on stackoverflow, so taking that into account I assume you can do this:

global $user;
$datefields = $form_state['values']['submitted_date'];
$submittedDate = "{$datefields['year']}-{$datefields['month']}-{$datefields['day']}";
$timezone = $user-&gt;timezone;
$newdate = new DateTime($submittedDate, new DateTimeZone($timezone));
$unixts = $newdate-&gt;getTimestamp();


This would require the user to have set his/her timezone accurately in the account settings.