[simonh]

In this case I think the valuations are justifiable.

Imagine that all the people that sent a Whatsapp message in the last year were charged SMS rates for the messages they had sent. How much would that cost them? Well, that's a reasonable rough measure of the value they have derived from Whatsapp. It's an important service that has real immediate benefits for the people using it right now.

SpaceX is a fantsastic venture, I'm very excited by it, but right now it's providing limited economic benefit. The Space Station is an expensive waste of money. A few comms satelites is great, but there haven't been all that many of them. Now, if SpaceX does manage to recover and re-utilise it's boosters that willbe a game changer. Their value will skyrocket (appropriately) and Google will make a killing on their investment. But that hasn't happened yet.