So, what is turning it on and should I be worried that it staying on, generating so much heat is not good for the unit?
Before the Take 2 upgrade the "Stand By" function was almost an Easter Egg. There was no documentation, but I found out from the 'net that what one needed to do is press and hold the "Menu" button for five seconds to stand by. I figured Apple intended to have AppleTVs always on. Having said that, when on they do run hot, but that's what the aluminum case is for - a giant heat sink.
As for why it turns on intermittently... I haven't checked, but it probably comes on when you launch iTunes (auto sync) on the host computer and/or to check it's Software Update.
I've watched it many times when I plug in my iPhone and iTunes launches, but it has never come on while the phone is syncing, nor has it ever come on when the Apple TV itself is syncing.
It comes on in the middle of the night when the host computer, my MBP is asleep. I'm glad to hear the heat is not an issue, but it sure does get hot to the touch. In spite of it all, I really enjoy my Apple TV.
I don't think "Standby" mode on the Apple TV is quite the same as it is with our computers. The unit never really powers itself down. I think it just spins the hard drive down and sends a black screen to the TV. Hardly standby. But if it makes you feel better, mine turns itself "on" all the time. My guess is the IR sensor responds to just about anything to activate the unit, or the unit it trying to phone home for updates.
As others have mentioned the AppleTV never really goes "off" or even to sleep for that matter. It's more like having the screen on a computer shut off. Somewhat annoying, really. It really needs a proper power switch (I know, I know: It's not aesthetically acceptable to Apple .)
The only times I have found my AppleTV coming on on its own is when there is any sort of power bump. Doesn't seem to take much to either make the machine wake up or reboot.
I used to have mine using the wireless network and it would get uncomfortably warm. Since hooking it up to an ethernet cable it is still warm, but distinctly less so than before.
pain in the frickin backside - I agree about the random turn on and the heat - in fact, agree more that it doesn't seem to really go off - the latest these days is the the pilot light in front goes amber instead of white and it seems to be in some arbitrary zombie mode - with the latest s/w updates, at least seems to transition out of zombie mode fairly gracefully - in the past, I've had to hard reboot the sucker.
__________________ We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology. ~Carl Sagan