[jamessb]

This doesn't seem to be true. This site [1] lists many agencies (based in the US, UK and other countries) that will sell you a passenger ticket for a cargo ship.

Availability is probably limited though, as each ship can only take a few passangers: "Cargo ships can carry a maximum of 12 passengers although most vessels only have accommodation for 4 to 6 passengers" [2].

[1]: http://flightlesstravel.com/plan/cargo-ships/

[2]: http://www.cargoshipvoyages.com/WhatToExpect/

[Animats]

You're right. Things seem to have opened up a bit. For a while, security was a big concern. CMA CGM will take passengers on some freighters. Maersk, the biggest line, won't.