which node will return something like
This is all that is added by Node.JS.
rm -r bin/node bin/node-waf include/node lib/node lib/pkgconfig/nodejs.pc share/man/man1/node.1
Now the only thing I don't know about is npm and what it has installed. If you install npm again into a custom path that starts off empty, then you can see what it adds and then you will be able to make a list for npm similar to the above list I made for node.
In Ubuntu 12.04 simply type this
$ sudo apt-get remove nodejs
It will uninstall nodejs and npm as well simple.