There are a lot of increasingly shrill remarks out there about how everyone should be doing open source projects in their 'spare time', so no-one has any excuse not to have a track record of FOSS contributions... frankly, it's bullshit.
I work in a closed-source shop (for some very good reasons, we can't open) and our devs do sterling work of a sophistication not seen in most projects, open or otherwise, solving a very difficult and rather open-ended algorithmic problem. On a good day, we get a lot of sophisticated work done.
Strangely, at the end of one of these good days, no one wants to go home and write a big fucking pile of code - we have girlfriends/wives/families that haven't seen us for 12 hours and probably aren't going to want to use the remaining hours (and typing time) to write MORE code. Even if that was a good idea - we are paid for full-time work here which means ideally we go home and relax, not flail away on endless side projects.