Slightly off topic: I saw an interesting presentation once where the presenter complained that modern day developers are expected to do open source projects in their spare time in addition to all the work on the job and ended by saying construction workers don't have to do open-source jack-hammering. It is a bit unfair.
many folks raise their public profile in professions by donating time to causes - builders donating free rehab work in low-income areas or for schools/churches, accountants doing pro-bono work, etc.
When I hire a carpenter for some building work, I'd rather hire somebody who has built his own house, or at least renovated an old one into something homely than the guy who lives in a derelict trailer.