I googled to find out if there was a problem with leaving butter out, and the answer was no on every one of the six sites I clicked to. The only time it might be a problem would be if all the moisture had not separated out of it when they were churning the butter. Otherwise... there's nothing about it that should go bad at room temp.

Kathy, I did see on several sites that if a stick of butter has been in the fridge for very long that it will likely have picked up some odors/flavors from other items in the fridge. Apparently when butter is at a refrigerated temperature and hard, those odors/tastes are not released, but at room temperature they could be. The sites I saw indicated that butter in and of itself wouldn't develop any smell or flavor all it's own without the presence of those other foods to effect it.