Maybe this is paranoia, but I'm beginning to find a lot of threads like this (and a few yesterday about 'how to hire people') actively coercive: "Contribute to Open Source or Don't Get Hired". 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…
That said, I don't see anything wrong with wanting people that have some open source contributions. It doesn't have to be anything along the lines of having written the linux kernel in your spare time. However, it should be something that you put serious time and thought into.