When it comes to cars I say don't let it idle because it's a trade off between the heat-output at low RPM VS the wear at that RPM, so I feel that it takes such a long time to reach the optimal temperature just sitting there it's probably causing as much if not more wear than if you just drive it outright. Not anything crazy but low load, low rpm until the oil is hot.
On a truck on the other hand, they only go up to around 2000rpm so it's likely best to let it idle.
As mentioned before a engine wears more in the few minutes it is cold, I actually read that it wears more in those few minutes it's cold when you start it up then it will with you driving it to Cape Town from Johannesburg when the oil is warm.