Someone sent me the following quote the other day by the designer of the GNU / Linux kernel, Linus Torvalds, and I thought it was a really accurate and meaningful quote. Some of the best developers I have ever worked with are people who are very passionate about software development and do it because they think it is fun.
Most of these developers also have their own personal pet projects that they work on, be it a phone app, computer game, website, or some other general geekery. One developer I work with has done a lot of algorithm work with fractals. When I am recruiting developers, the one thing that leaps out at me on their CV is whether they have a pet project. If they list it on their CV, then I always ask about it, as generally you will learn a lot about a developers abilities by hearing them talk about their hobby project.
I am not saying that any developers who don’t have pet projects are bad. Far from it, I have worked with many good developers who don’t code in their spare time. But, the programmers that do have pet projects tend to be better, well rounded, developers in my opinion as they go out and seek new technologies and experiment.