You should definitively put 3rd party libraries under the source control. Also, you should try to avoid relying on stuff installed on individual developer's machine. Here's why:
- All developers will then share the same version of the component. This is very important.
- Your build environment will become much more portable. Just install source control client on a fresh machine, download your repository, build and that's it (in theory, at least :) ).
- Sometimes it is difficult to obtain an old version of some library. Keeping them under your source control makes sure you won't have such problems.
However, you don't need to add 3rd party source code in your repository if you don't plan to change the code. I tend just to add binaries, but I make sure only these libraries are referenced in our code (and not the ones from Windows GAC, for example).
