I've always put cooked food, be it meat, pizza, soup, stew, roasts, you name it -- into the refrigerator while still hot. Not fresh off the boil, mind you, but at least a half-hour off the heat source.
I realize that this will heat up food next to it, but the problems with that seem to be to me negligible.
Yet some insist that you should wait until the food has completely cooled down to room temperature before they refrigerate/freeze it. I see no scientific explanation as to why this should be so. I figure, the faster something cools down, the better, as room temp is right about the region in which the bad bugs really thrive.
Any arguments, pro or con? (I once had a girlfriend who always left food out overnight -- uncovered. It was completely gross, and when she suggested that we have that again for dinner, well, you can see why she's an ex.)