* Fast. Everything is fast (attribute to Google v8 and node guys). REPL opened in a twinkle, tests finish before I grab my teacup. No more waiting for "warm up".
* NPM. It's so good. I like the idea to install all dependencies locally in project directory. Mentally, dependencies are part of your application, it make sense for them to live together. Physically, put dependencies in project directory will solve dependency conflicts between applications naturally; besides that, it enables you to jump into deeper (library) code more easily, if you use a decent editor like vim or textmate, because all files are in one place so a simple search will find them all.
* Library boom. Maybe a requirement to success, but it goes a little wild. In some area like testing, tons of immature tools are there, no one can tell a best practice. I have to examine all these tools to find a best fit to my project. I really miss something like rails guide or ruby-toolbox.com here.
* Asynchronization is still hard. It's hard for the same reason GOTO statement is hard, or lazy evaluation is hard. It messes up my tiny little brain easily by disrupts the execution order. The weird exception backtrace only make the situation worse (however this should be fixable). The little piece of asynchronous code is like virus, it gradually infects the rest parts of your application (IO monad: ah?). The co-routine tricks/tools people used to dress asynchronous code up to synchronous code still looks awkward (and here's another area suffers the library boom problem). I will be very careful if someone propose to write an entire application in node, it would be better if I can restrict asynchronous code on a small land. I bet node is better in polyglot paradigm, e.g. node as my ajax push server, rails to power most web pages.
Node is great! Be careful with asynchronous calls!