Cold butter is tough to spread, but if you leave butter out then you risk it going bad sooner.

Apparently there are European-style butter crocks that solve this problem! Did not know that:
http://www.organicauthority.com/foodie-buzz/should-you-refrigerate-your-butter.html

Personally I don't leave butter out, but now I'm wondering if maybe I should get a butter crock and start doing so!

Do you leave your butter out? Does it ever go bad?