Well, I had read in previous posts that it wont do it if the box has seen activity within the past 15 minutes.. But I'll frequently leave the TV on as background noise either on the news or a music channel or whatever, and not pay attention to the screen..
Put it this way -- I picked up my Tivo a week ago, and its done it to me 3 times now so far.. I just think the option to restrict it to suggestions when both tuners are not recording anything would be helpful (I cant be certain if the first tuner was recording another suggestion, or one of my wishlist things when it did it)