While I'd never say I "own" a pet (anymore than I would say I "bought" a pet: I "have" a pet...like I have a friend or a mother, etc., and I "adopt" a pet), I am now sharing my home with four cats, which has been my limit so far (though I prefer 3).
Well, my "limit" is perhaps soon to be 5...yikes!...as one of the cats at the shelter I volunteer is on the euthanasia block: not because he's old, or ill, or mean (he is about a year old, very sweet, good with other animals, healthy except for a pot belly!) but because he's a real scardy cat, and they don't think he'll do well when they move him to the "adult" room (not a place for renting porno films, but one of the three cat rooms my shelter has). I personally wouldn't care if he hid under a sofa for a month, but not all potential adopters are as tolerant (one cat was brought back after a WEEK because he didn't want to come out of a closet---and he was euthanised!)