It did happen to me. I'm not "scared it will happen" -- it already did.
Neither I nor anyone else used the word "overheat." (Edit: G&W did. Oh well. He edited that since I read it.)
Not the most attentive reader?
Also, it's hardly a key feature if I've been getting along just fine without it for months. All those messages from Nintendo were annoying anyway.
If you don't like to receive messages from friends or DLC on Animal Crossing and such, then go for it. I, on the other hand, do, so I keep my WiiConnect24 on, and nothing's ever happened to me. And hot, warm, overheated, whatever. Whatever temperature my Wii is, it's perfectly fine.