Having been interested in the old-time American hobo lifestyle for some time, it has come as a great surprise and pleasure to find a thriving subculture of modern hobos still riding freight trains across the US. PBS has a superbly evocative film about hobos here.
Indeed, some old-timers are still out there migrating by freight-train to find work but there is a new wave of hobo riding simultaneously. It would appear that the new younger generation of 'bos' brings a decidedly 'punk-attitude' that simply rides the rails just for the sake of riding the rails - wonderful stuff. This creates an amazing mixture of young punks and old hobos doing the same thing, just for different reasons.
Riding the rails is also referred to as 'freight-hopping' or 'train-hopping' and there is quite a bit of stuff out there. Railroad Semantics is the website of Aaron Dactyl who publishes his own 'freight zine' about his adventures and is well worth a read. Northbank Fred has a very comprehensive website that has loads of hobo stories and links.
There is also a ton of stuff on YouTube and I particularly liked the videos from Wizehop.
Sarah George's documentary Catching Out is also a good all round study of the modern hobo. (Isohunt torrent download).