Curious... That time isn't even Standard Time for America/New_York at the moment. I have PM display times in my local time zone (currently EDT, same as America/New_York at the moment). That tells me that your reply was posted at 2008-09-19 16:10:07 EDT, which would be 15:10:07 EST, yet you show 17:15:48 from DateTime->now. That's about an hour off, but it's in the wrong direction.
What does Windows think your time is (and might as well check it's notion of the time zone, too)? I'm stretching here; I don't have a Windows system that I can use to check this.
Update:One other thing that might be worth checking:
my $isdst = ( localtime(time) )[-1];