I worked on a Google.org project (my company was the beneficiary), and our time spent with Googlers was their designated paid CSR days (we're not even talking 20% time). They were fully expected to be always-on, taking calls and completing work to deadlines during their "volunteer" hours with us. Their contributions to our project were of very limited value, not through any fault of the individual contributors but just through the fact that they weren't really allowed any headspace to engage with our project.