I am seeing a lot of buttercream recipes that contain milk and the directions say it can be stored at room temp. What about the milk... couldn't it go bad if left at room temp?

The sugar stablizes the milk that you use in the recipe. You can keep it for a couple of weeks before it needs to be thrown out. However, some people do like to stick their icing in the freezer and then just give it time to thaw.

So... you can keep it at room temp for a couple of weeks? Really?

Yeah.. I do it all the time. I just have to re-whip it.