This hour-long demo is worth watching. I haven't been so amazed since I saw Scott Davis demonstrate Groovy at JavaOne 2009.
The only downside (not to me, though ;-) is that Node currently only works on Unix-like systems (Linux, Mac) and not yet on Windows. You also have to compile from source (no binaries yet), which is not a big deal because you only have to type "./configure". "make" and "sudo make install" one after the other in the main directory once you've unzipped the tar.gz file using "tar zxvf node-VERSION.tar.gz".
Refcards has a reference card for Node.js.
There are some great possibilities here, such as when you combine this with E4X.