I travel a lot, probably 20 times since 9/11 and its further applied security proceedures, and have always used locks on my checked luggage. I use the combination locks as they are easy to remember, we don't have to fumble with keys or find them missing when needed. BUT, I do not lock them down on the checked luggage. I place them through so that all they need is to be squeezed down. Then I ask KINDLY to the ticket agent to ask TSA to lock them after inspection, and SPIN the dials - they ALWAYS inspect our bags. I then sit there at the ticket counter (to the side so others can continue their check-in of course) as TSA goes through its inspection and I watch them go through, and sometimes ask the officer who's nearest me to remind them to lock it, PLEASE, as they are finishing.
I'd say 75% of the time, they do SPIN the dials, but not always. 
This proceedure is not perfect by any means, but I've never had a problem. Later I've found the "inspected" letter mentioned earlier inside, but my locks have always been in tact. I do bring along extra zip ties just in case.