Being a good software developer implies several things like knowing a couple of languages, knowing some design patterns, but mostly having some experience. What you learn in school and what is done in the businesses are farther then the day I’ll wear a moustache. But, not all experiences are good ones. Some should make you progress in your constant quest to the absolute software Truth and some make you regress.
Lots of companies still handle bug tracking on sheets of paper (or at best on Excel) and use Windows file sharing as their source code control system. What’s an experience at a place like that worth ? And maybe when someone talks about his experience of Reviewing the documentation process, what he really meant was copy-pasting links in Word documents.
How can you evaluate one’s experience value ? By evaluating the products they’ve made on their previous company web-site ? Ask them to write code ? I don’t think so. Software development is a lot more then coding and releasing products. It’s about how you handles change request, bugs, tasks, estimating, features, source control, documentation, tests, code review, etc. It’s about lots and lots of things that you can’t judge by a final product or KLOC. You’d really have to work for a company for a certain time to know if they are good enough.
Open source projects are… open. You see how they handle bug tracking, documentation, source code control, build process, etc. All this is public. All successful open source projects have great developers involved, voluntarily. Which means, they’ve evaluated how the project work and agree with it or change it to fit the need. If not they just leave or let the project die!
It is less risky to bet on open source project experience then (closed) company. So don’t be afraid to put it on your resume. Or else, it’s never too late to start getting involved in one of those project