I work for Pivotal Labs. For engineering hiring we do onsite pairing interviews that last a day, divided across two teams. Whenever possible, which is most of the time, on a real task on a real project.
The disruption is worth it, because engineers get to pick their peers.
I work at Pivotal Labs also. I don't even find it that disruptive to interview candidates on our projects bc I'm still working on what I'd be doing that day. It's certainly less disruptive than marching our entire team one after another into a conference room where they grill the candidate for an hour at a time, which is what most employers do.
