i'm not sure i believe anyone who says they prefer someone that grows on them. it's an ideal situation to have an immediate attraction, physical or otherwise, but probably more often than not, someone you're not initially attracted to comes to grow on you. personally, i'd prefer it if i were immediately attracted to a guy, but because i tend to be extremely untrusting of men, it can take a while for me to fully admit i'm into someone. the worst is when you admit you like someone, and then he/she ends up being an asshole and thus loses all physical appeal, but still thinks you want them.
i'm more into someone's personality attributes and values than looks, so i'd say that nearly all of the people i've been into have been people i've come to see as attractive in time rather than immediately.
in other news, i just threw out a ton of condoms that expired over a year ago, so clearly i should be offering no relationship advice to anyone ever.