Ryan Bates' Railscasts (http://railscasts.com/) are uniformly excellent short introductions to different topics, and a great example of how to do screencasts right. They're short, give a quick overview of a new and relevant topic, and you can pick up a lot of little tips and tricks on how to develop in general as you watch him code (especially if you use the same tools).
They're a great way to get jumpstarted on something you've never approached, after which you're in the right frame of mind to jump into the docs, since you will have grokked the general overview of the topic from Ryan's short summary. YMMV, but I find it much easier to get an overview quickly than hitting a pile of docs cold.
They're a great way to get jumpstarted on something you've never approached, after which you're in the right frame of mind to jump into the docs, since you will have grokked the general overview of the topic from Ryan's short summary. YMMV, but I find it much easier to get an overview quickly than hitting a pile of docs cold.