Wolfram Programming Cloud is now up and running, for anybody interested. Speed seems to be particularly slow right now, presumably because it just went live and there's tons of traffic.

Here's a quick intro for programmers. It's also supposed to be pretty easy to pick up for people with little to no programming background.

EDIT: This appears to be a step-by-step comprehensive guide to the language. For some reason I couldn't find any direct link to this page.