From here I think I’ll start playing around on a sandbox. Each of the distributions offers a way to spin up a VM or log into a cloud based environment. There are also docker images out there. (search hadoop, cloudera, or hortonworks). Most of these docker images look fairly new, so don’t cut yourself.
I’m looking at the HortonWorks distro, so I’ll probably setup a Hortonworks Sandbox.
Jon includes some resources he’s used to learn a bit about the topic. I think he’s going down the right path with videos and mailing lists—the ecosystem changes too quickly for books to have much long-term value, and mailing lists & forums tend to be better for keeping up to date. My biggest suggestion is to get case studies and play around. Check out studies on e-mail ingest, real-time data analysis, and analyzing fantasy sports for starters.