Where can I find the source of Nautilus? I'd like to play around with its source code and compile it. What's the best way to go about this? Obviously, it would be nice if I would easily be able to revert to the repository version if something bad happens :)
If you want use the same sources from the installed version you must get it from the Ubuntu repository.
First, from the softwate center, software sources, you need to enable the "source code" sources.
Then you can use
apt-get source, to get the source, and
dpkg-buildpackage, to build the package.
Check the following link for details. http://www.debian.org/doc/manuals/apt-howto/ch-sourcehandling.en.html
It seems you don't need to install it and can test it by running it from the source code directory. This means you can keep your installation while testing your modifications.