Geeez, getting all worked up about a simple thinkg like that!!! Simple, neither extreme is good. Don't idle for 10 min - waste of fuel, and don't idle for less than 10 sec - damage. Of course, the temperature affects this value. Of course, if it is below 0F you need to give it 1-2 minutes.
Here in Ottawa we are below 0F most mornings. I am pretty sure that many/most drivers don't have the patiences and simply don't care about engine noise, but get into their cars and gun it. I get passed all the time! Consider women driving their kids to day care. You think she is going to sit in the car letting engine warm up while children are freezing in the back? #@$%! no.
As I don't see too many stalled cars here I have to assume that engines are very resiliant to both kind of abuse - too little and too much idling.
As everyone pointed out, there are different method and approaches. There is no single answer. I myself use anywhere between 20 seconds and 10 min. Tonight was cold so this morning I let the engine idle for about 10 min while dropping off kid at day care. That way I can drive to work at full speed. Going back home it is warmer. I only give it about 20 sec and simply drive using minimum load. I have about 10 klicks to highway, plenty of time for engine to warmup. So it all depends. Are you in a rush? Is traffic light and you can drive slowly? etc.
Regardless of engine damage, excessive idling is simply a huge waste of fuel. I don't care how little it costs, there are a lot of young men in Iraq fighting for it and we owe them to try to minimuze our consumption. If your #@$%! is cold then dress better, use more layers, etc. Sure I have problems with frost and ice and visibility, but I always manage without idling for 10 minutes.
Anyway that is my 2c.
