I've traveled on lots of amazing rates in the past, and I've never once thought about calling the airline or hotel. (Besides, if you don't have access to an elite-status line, what are the odds that you can even get an agent on the line without a long hold?)

The only one I think is unethical to pursue is the one about the internal rate. At least with Marriott, you can log in and few lots of zero-rated rooms. The rate rules always specify what the rate is for - usually some sort of certificate stay. It's clear that the guest isn't to book it and expect a free room.

But for a Travelocity hotel booking or any type of airline booking, if I see a rate there, I'm going to assume that it is there on purpose. After all, if the "mistake" happens once, they I might believe it's a mistake. Bad software testing or whatever. If it happens twice, then it's no longer a mistake. If I ever get lucky enough to find one of those Ryanair zero fares, why should the burden be on me to call them and double-check that their software is functioning correctly? (And if I do, will they even answer the phone?)