When I'm talking on the phone on Bluetooth headset, I like to turn the screen off and put the phone back in my pocket. But the stupid power button hangs up my call! And if I wait long enough for the screen to turn off by itself, I can't turn it back on to check something without hanging up. Even a double tap to wake up will hang up call. come on, really!?
Also, I'm surprised incoming phone calls can't be made non-intrusive. When the screen is on, an incoming call should just be a small window in the corner of the screen, with a single vibration. That way I can continue filming the alien spaceship or whatever even if my wife calls me to tell me to buy milk. Having the call take over completely when I'm already using the phone for something else is just dumb. My old Palm Pre handled this perfectly.