I used side projects mostly for idea validation. For example, I am working on an MDSD system that takes a UML or RDFS model and generates a web 2.0 app written in Google Closure and using XMPP to interact with the application layer. All of these technologies show great promise but none of them have really taken off. http://www.dynamicalsoftware.com/mdsd/closure is where I have documented some of my findings so far in exploring the merit of these three technologies.