Was contacted by their technical recruiter via LinkedIn, had a followup phone screening with recruiter, followed by a followup phone screening with CTO and one of their engineers a few days later. Was called in for a 6-hour on-site interview the following week; I was to start with a 45-minute presentation of my own devising with some suggestions from Pivotal (put your best foot forward, show your depth, etc.), to be presented to the whole (albeit small) company. After that was a short tour, lunch, then individual interviews with key team members with whom the position would interface. Overall, this was a unique interview experience for me, but also gave a much better opportunity for mutual evaluation. I would rate it as more difficult than interviews that I've typically been involved in, but it helps set expectations. The process is definitely geared around carefully selecting key talent in this startup phase, which makes sense.