I don't.
My day always used to say that too much weight on the car keys could cause damage to the ignition key socket - but then he told me that when I was a wee kiddy, and I'm almost 40 now
I just get in the habbit of having a single key plus fob on my car keys and the rest of my "bunch" seperate.
My house key is attached to my car key but that's it. It stays in my pocket anyway as I have keyless entry / start.
Do you keep your car keys on your normal keys?
Everything on one key ring. I'd end up leaving house without one set of keys otherwise. If I cant drive my car without bringing my house key along for the ride, then I'm safe from doing that!