Has anyone ever traveled with an expired passport?

Ok we are going on a cruise in the beginning of July and I just noticed that DH's passport expires next month. I know that he could probably do it now by mail but i'm nervous about that, even though it takes 4-6 weeks.

My question is can he travel with an expired passport? We are going on a carnival cruise to puerto rico and the virgin islands. I went on carnival's website and unless i'm reading it wrong he can go with and expired passport as long as it hasn't been expired for more than 10 years, I called carnival and they said the same thing. So this morning i Called my travel agent to double check and she tells me to have him bring his original Birth certificate and drivers license. She also said he should get his passport renewed even though he could still bring his expired one. I don't know who to believe now.