I have, and then I've left them off. I've used them and had them removed and never returned. (I call that stealing but what ever). I love to get my bags saran wrapped when we fly internationally.
Molly
Lula '06 outgrew her allergy to milk & eggs, still allergic to peanuts and cats
Dolly '10
A lock doesn't deter the average thief with a ball point pen - https://www.youtube.com/watch?v=wpIJVWXsBBI
EricaDD 1/05
DS 9/08
Since one just does not simply walk into Mordor, I say we form a conga line and dance our way in.
Excuse me, are you in a play?
I fly pretty frequently (at least a dozen times a year) and have never locked a suitcase. Even when we're flying as a whole family, we almost never check bags, but when we do we just put our valuables in our carry-on. I'd imagine that a thief would be more likely to just take the whole suitcase and go through it at their leisure offsite, rather than rooting through it, then closing it back up and replacing it. I also have never had a bag pop open when it's checked (although I have had straps/handles ripped off by the machinery).
DH and I fly about 200-250k per year total and never lock a suitcase. We keep valuables with us and when we check bags never have issues.
DS #1 Summer 05
DS #2 Summer 07