Hi there
I just tried to power my Arduino Micro via Vin using 12VDC from a regulated lab power supply, this resulted in smoke and a bump on the Atmel 
I just measured what comes out of the power regulation circuit and this thing doesn't seem to work at all. I only get a drop of about 1.4V between the Vin Pin and the 5V rail. Normally I would consider this a dead on arrival, but interestingly there are a bunch of reports about this problem in other forums as well (e.g. http://forums.adafruit.com/viewtopic.php?f=25&t=35157 , http://www.adafruit.com/forums/viewtopic.php?f=25&t=35387 ).
Can it be that there's a serious problem with these things ? I just try to figure out if it is T1, T2 or the regulator itself. As mentioned in this thread: http://www.adafruit.com/forums/viewtopic.php?f=25&t=43482 T1 seemed to be faulty, I just try to figure out if this is the same case here but I don't really feel comfortable about this.