The comparison with Uber and Whatsapp is not the proper one. These are private companies that were funded and acquired, respectively, purely on growth potential.

OpenTable has been a public company for almost 5 years now (see http://finance.yahoo.com/echarts?s=OPEN). Revenues, cost, growth, and all other metrics have been publicly examined and scrutinized for long time. The 46% premium paid by Priceline is based on how the new management estimates that they can leverage the assets of Opentable and hardly a "bubble-ish" premium.

If you believe that OpenTable is part of a bubble, then the whole US stock market is in a bubble, which may be true but again not directly connected to Uber and Whatsapp valuations.

I think Uber's valuation makes the most sense out of all of the ones we've seen thus far. They're poised to completely eliminate the taxi industry in its current state.

Without noticing it? People have been screaming "bubble" for years now.