But $1 billion? I'm not sure if that evaluation is entirely justified. It has a pretty large user base, granted, but there's practically nothing that warrants people will continue using it in the next 5 years.
It's far from the best messaging app, but definitely the most popular (in Europe).
i work on an im client[1], and my mom sent me a link about whatsapp :)
[1] to be fair, verbs.im is a gtalk/aol/yahoo multi-protocol client. infact, one day we could wrap over whatsapp as well. not exactly re-building a new graph but re-using your existing lists.
I think this is a great example of why you should never be afraid to try and reinvent something. Even a concept as simple as messaging apparently still had a (potential) billion dollar opportunity.
I would be amazed if they're doing $100M/yr but who knows.
One thing that worries me with Google's purchase is the ads. Google will want to introduce while I would prefer to pay the annual fee and keep it ad free. Let's hope that doesn't happen.