There were other reasons we decided to be a little more cautious about committing to this kind of initiative. As Toby Negrin pointed out recently: There is one major difference between the companies involved in DERP and ourselves -- they all use data collected from their users to make money and we explicitly do not. This is frankly a point of pride for many members of the foundation and certainly the community.
Wikimedia is a nonprofit, but that doesn't mean it can't bring in money based on data collected from its users. I think we all know that this is exactly what it does. As a non-profit WMF is just prevented from making a profit, right?
More pragmatically, the last week of organizing for the DERP launch just happened too fast for us (and happened during Wikimania, to boot!). Those of us in research-y roles hadn't had a chance to discuss all the evolving details as a team, and on the eve of the launch we didn't all feel we had a 100% clear idea of what commitments we would be making by joining.
Ok, this is much more plausible. I'm new to the idea of DERP, but based on what Stuart just wrote it does sound like a useful effort to be a part of.