B.

I'm kind of lurking here on the United site; I mostly fly USAir, which also has SWUs. And USAir used to be notoriously forgetful about collecting SWUs (although they seem to have tightened up considerably over the past couple of years). When this first happened to me, I decided to turn in the certificate anyway -- not necessarily out of integrity, but largely out of concern that in a subsequent mixup I could lose my Business Class status. When I told the gate agent that she needed to collect my certificate, she was VERY profusive in her thanks, telling me that she could have lost her job if my ticket had been audited. I've never felt that hanging onto my SWU was worth someone else's job, so I've been scrupulous about turning it in since.