DH and I have ours, thank goodness, we renewed them for our first DCL cruise in 2001 and they're still good.
We did ours for our 2003 cruise so we're still good too!
Everyone that is going to get passports, double-check before going to the Post Office - ours does passports by appointment only. So it might not be a bad idea to call now even you weren't planning to do them for a month or 2 as I have heard it is sometimes taking that long to get an appointment.