Definition of a short trip?

[blktoptrvl]

With apologies to John Mellencamp…

I am living in a small town. So small that your average trip “across town” is 5 miles.

When I first moved here, I was staying 3 miles from work – not far enough to let the car warm up; so I moved another 4 miles further away.

7 miles is just enough distance to get the temperature indicator to the center of the gauge.

So, how short is too short a drive?
How far do you have to drive to avoid crankcase ventilation problems?
And if you can’t avoid the short trips, what do you need to look for as a sign that your engine is in mortal danger?