Never limped KK in my life.
You'd need 8 limpers to build the same pot that you get if you raise 4x and get just one caller... Nevermind that you probably got outflopped at that point. If it's important for you to win a lot of hands then go ahead and limp KK. If you want to make money, I suggest your raise it every time. At some point you need to get the money in. It's much easier if you already built a pot.
There are some special situations where you could limp, but those are so rare, that I really don't want to get into it.