We're going with the open core model ourselves. In our case focusing on commoditizing our competitors by giving away the algorithms while at the same time enabling companies to build their own solutions.

One interesting aspect of open source is the pitch for enterprise. It aligns your business model with the consumer's needs and if it's close to data (storage or analytics) the risk of a company going under or getting acquired doesn't leave them in the dust (ala apple/foundationdb)

Open core (like cloudera worth 4x horton) allows for the best of both worlds where you don't leave your customers locked in but you can still get licensing fees for added layers on top.

Edit: Let me clarify a bit. Open core is for company's who just want to pay for solutions also allowing them to serve companies who want to build their own infrastructure. There's some amount of lock in with open core, but if the core infra is open source it still allows the customer an easier migration path. In our case we went with an apache license for the core tech and sell a layer on top that allows for easier deployments.

While open source startups are rare I think it's critical for core infrastructure to be open source.