No - I don't think you should put third party libraries into source control. The clue is in the name 'source control'.
Although source control can be used for distribution and deployment, that is not its prime function. And the arguments that you should just be able to check out your project and have it work are not realistic. There are always dependencies. In a web project, they might be Apache, MySQL, the programming runtime itself, say Python 2.6. You wouldn't pile all those into your code repository.
Extra code libraries are just the same. Rather than include them in source control for easy of deployment, create a deployment/distribution mechanism that allows all dependencies to easily be obtained and installed. This makes the steps for checking out and running your software something like:
- Install VCS
- Sync code
- Run setup script (which downloads and installs the correct version of all dependencies)
To give a specific example (and I realise this is quite web centric), a Python web application might contain a requirements.txt file which reads:
simplejson==1.2
django==1.0
otherlibrary==0.9
Run that through pip and the job is done. Then when you want to upgrade to use Django 1.1 you simply change the version number in your requirements file and re-run the setup.