We had Shelties when I was very young, and my mom has Shelties -- well, one now; the elder guy passed a month ago -- and I've never noticed a strong herding instinct in them. We'll still have a cat or two and they'll make for reluctant sheep if need be. :)

But yeah, I think you're thinking of Border Collies as shalmestere says. Every BC I've met has been super sweet, but I don't want that intelligent or intense a dog.