Should you commit .gitignore into the Git repos?

Normally yes, .gitignore is useful for everyone who wants to work with the repository. On occasion you'll want to ignore more private things (maybe you often create LOG or something. In those cases you probably don't want to force that on anyone else.

You typically do commit .gitignore. In fact, I personally go as far as making sure my index is always clean when I'm not working on something. (git status should show nothing.)

There are cases where you want to ignore stuff that really isn't project specific. For example, your text editor may create automatic *~ backup files, or another example would be the .DS_Store files created by OS X.

I'd say, if others are complaining about those rules cluttering up your .gitignore, leave them out and instead put them in a global excludes file.

By default this file resides in $XDG_CONFIG_HOME/git/ignore (defaults to ~/.config/git/ignore), but this location can be changed by setting the core.excludesfile option. For example:

git config --global core.excludesfile ~/.gitignore

Simply create and edit the global excludesfile to your heart's content; it'll apply to every git repository you work on on that machine.

I put commit .gitignore, which is a courtesy to other who may build my project that the following files are derived and should be ignored.

I usually do a hybrid. I like to make makefile generate the .gitignore file since the makefile will know all the files associated with the project -derived or otherwise. Then have a top level project .gitignore that you check in, which would ignore the generated .gitignore files created by the makefile for the various sub directories.

So in my project, I might have a bin sub directory with all the built executables. Then, I'll have my makefile generate a .gitignore for that bin directory. And in the top directory .gitignore that lists bin/.gitignore. The top one is the one I check in.