A great way to get comfortable with node.js is to read github projects that are using it. I've got a few at github.com/dpritchett but I'd particularly recommend anything at http://github.com/jashkenas . Dig into some of the NodeKO winners and see if you can find source code, too.
I would go so far as to say that the greatest strength of node.js is the way people crank out interesting and possibly useful code and stick it on github. This makes it very easy to dive in and start hacking.
I would particularly recommend checking out socket.io, and maybe some of the projects using it. It's a way of doing realtime browser-server communication, which uses websockets if the browser supports it, and a variety of increasingly ugly fallbacks on browsers that are old and/or made by Microsoft. You can make some very cool stuff with it.
Also, definitely get npm, the node package manager. It makes installing libraries much easier:
stephank's orona (html5 tank game) is a neat project: http://github.com/stephank/orona