1. A valuation expert thinks about What's App from a valuation and from a trading perspective.
Damodaran's trading perspective of looking at cost per user sounds plausible, but I wonder if the calculation was as simple as "Facebook messenger is going to be worth X% of the company in the future. Buying Whatsapp at least doubles Facebook's chance of dominating the message space, and X > 22% so it is worth paying almost 11% of the company for Whatsapp." Also, from a valuation perspective Facebook doesn't have to monetize users more than 1 dollar a year in the short term, they can keep Whatsapp's promise to be ad free for 5 years and only later start aggressively monetizing a greater user base.
He's trying to teach the idea of margin of safety, a long term perspective and investing in what you know, but it's interesting that in doing so he is highlighting investments that definitely underperformed Berkshire's book value as a whole. The farm is worth 5 times the amount it was bought in 1986, Berkshire stock is up over 5000% since 1987. The actual calculation is more complicated than that since the farm gave off earnings in the meantime, but the difference is still quite notable.
3. MTGOX, the original bitcoin exchange, is down right now.
It could be that they are insolvent or they are just particularly incompetent, but it is probably a combination of both. The coins on the exchange, which could not leave MTGOX custody, were trading at less than 30% of the value of bitcoin on other exchanges. It would be amusing, but highly illegal, if they were actually buying these discounted coins and arbitraging the difference on other exchanges to make it back to solvency.