Whatsapp is one of the most brilliant applications I have ever seen, and it hasn't even caught on fully in the United States yet. Travelling around South America, I have yet to meet a person with a cell phone who doesn't have what's app. It also doubles as a walky talky. It's worth the price and will gain in value.
I think when a technology is hot and in demand and mobile apps are in demand right now they will attract large buyout prices, some of these deals are worthwhile in the end and some end up disastrously for the company purchasing the company at such a high value but in the end with the proper due diligence these companies feel that they are worth the price they are paying.
Large companies like Facebook snatch up smaller startups like Whatsapp for exorbitant prices just to make sure that they do not eventually become competitors or fall in the hands of other competitors. The market values they are purchased for do not reflect what they might trade for on an exchange or what they could mean to consumers. It is simply a reflection of larger businesses playing chess against one another.
I believe Facebook over valued and over paid for Whatsapp to help cover the fact that Facebook itself is over valued. I do not believe Whatsapp was worth the high price that was paid for it and I believe that is exactly why Facebook pulled this trick. Watch out for another bubble in the tech industry.
I do not believe that tech companies like Whatsapp are worth the high prices that they are selling for. I think most of the companies buying such companies are basing their assumptions on the chance that the technology might become profitable in the future. But that doesn't always means it will.