I'd say that working on commercial side-projects is unethical. On the other hand, experimenting with code is exactly the thing you want your developers to be d

I'd say that working on commercial side-projects is unethical. On the other hand, experimenting with code is exactly the thing you want your developers to be doing in their down time. When working on commercial software you're subject to deadlines, management decisions, interoperability issues and bugfixes. This limits your creativity. It goes with the territory, so I'm not complaining here, but large parts of this process are Not Fun. Experiments on the side don't have these issues and allow you to do a little freewheeling. Keeps that whole hacking spirit alive. People without side-projects tend to move into project management, oracle db maintenance or turn into burned-out has-beens after a few years of software development.