format_date() not working with timezone - drupal

Question

Drupal 7.8 install
Site Timezone set to America/New_York in the region settings
I have this code in a page callback
Problem happens on multiple servers
format_date() is not adjusting for the timezone offset by either the default site timezone, or even when I add the timezone string as an argument.
Below is the code, and at the bottom of the code is the output commented out. There are 2 examples using format_date, and the last example is what I had to do to get the correct time to display.
Any ideas on how to get format_date() working with the timezone?
header('content-type: text/plain');
// utc_str as it would come from the db of a date field
$utc_str = '2011-09-01 14:00:00';
// converting to a unix timestamp
$timestamp = strtotime($utc_str);
// first print with format_date, note default site timezone is America/New_York
print 'format_date($timestamp, "custom", "Y-m-d h:s:i"): '. format_date($timestamp, 'custom', 'Y-m-d h:s:i') ."\n";
// next print date by actually setting the timezone string in the argument
// Result:
$tz_str = 'America/New_York';
print 'format_date($timestamp, "custom", "Y-m-d h:s:i", "America/NewYork"): '. format_date($timestamp, 'custom', 'Y-m-d h:s:i', $tz_str) ."\n";
// this is the only way i could get it working
$date = new DateTime($product->field_class_date['und'][0]['value'], new DateTimeZone(date_default_timezone_get()));
$offset = $date->getOffset();
$formatted = date('Y-m-d h:s:i', ($timestamp + $offset));
print $formatted;
/** This is the output
format_date($timestamp, "custom", "Y-m-d h:s:i"): 2011-09-01 02:00:00
format_date($timestamp, "custom", "Y-m-d h:s:i", "America/NewYork"): 2011-09-01 02:00:00
2011-09-01 10:00:00
*/

Answer 1

The way you have solved it is correct. If you use PHP 5.3 or higher you can use the DateTime::add method and simply add the offset, without making a timestamp from it like i did below.
$utcTimezone = new DateTimeZone('UTC');
$timezone = new DateTimeZone('America/New_York');
$dateTime = new DateTime('2011-09-01 14:00:00', $timezone);
$offset = $timezone->getOffset($dateTime);
print date('Y-m-d H:i:s', $dateTime->format('U') + $offset);