Developers Motivations - Why start contributing to Open Source Projects?

There is a huge amount of software developers who always have worked on privative software, basically, for companies that produce software .

However, as an additional task, it is interesting for them to understand why they should start contributing to Open Source projects.

On next video, Jessica McKellar, Open Source advocate, core developer of Python and member of the Python Software Foundation, and maintainer for Twisted and OpenHatch [1],  explains, among other stuff, some clear reasons about why someone should consider, at least, start contributing to an Open Source project [2]:

From Jessica's perspective, contribution to Open Source projects should be performed in order to:

1) Give back to the community. Above all, if you like a particular technology or project, you should consider start contributing to it as a way of restitution.

2) People. As far as she is concerned, smartest people she knows comes from Open Source project movement.

3) Education.  With a Master on Computer Engineering, Jessica recognizes not many lessons being taken on Software Engineering. Contributing to an Open Source project is a way of enforcing knowledge on Software Engineering, as well  as obtaining experience.

4) Work. Open Source contribution is a way of transparency and a "do-ocracy" way of showing someone's capabilities to people and companies hiring.

5) Enjoying. In the end, contributing to a community ends being an enjoyable thing.

The video also shows a complete bunch of topics on FLOSS contribution, as different ways to contribute. Apart from that, Jessica also explains on a very simple way the different technical aspects common to many projects, such as the Bug Issue tracker, the ways of performing changes in code and generating a patch, etc.

References:
[1] http://web.mit.edu/jesstess/www/
[2] http://www.youtube.com/watch?v=IXnNgLmd6BM