I hadn't heard of WhatsApp until a few days before their acquisition by Facebook. I can't say as I knew anything about it, and the $19B price tag for the acquisition still seems ridiculous.
In the latest The Talk Show, Gruber is talking with Ben Thompson of stratechery (incidentally, why did I find out about this via stratechery, before is showed up on daringfireball or my podcast RSS? In fact, it still hasn't shown up on daringfireball) about the acquisition, and they talk about value per user of the acquisition, and that feels like a flawed metric to me.
That is, there's a per-user value, but it's proportional to what you can get for them. When your foreseeable cap is $1/user/yr, it's a pretty low number. They talked about value per user compared to facebook itself; well, facebook users are worth a lot more. Advertisers know much more about them, and it's much easier to put ads in front of them.
WhatsApp claims to be (and I've no reason to doubt them) against advertising, so I'm not sure that they have anywhere near the value of users in other social networks (compare with Skype, for instance, where you can monetize (some of) their communications).
Anyway, the point is that it still seems a bit crazy to me.
Although I was amused to note that my wife, being from Hong Kong, watches Hong Kong TV. After the acquisition, she told me that some of the TV shows she's watched recently have mentioned WhatsApp, but she (and her parents, who are visiting us) had no idea what they were talking about.
The one thing I wonder about (and this just occurred to me as I was writing this) is if there's a long-range play being made by facebook to link WhatsApp accounts with facebook ones, which would allow mining the communications for more targeting of people with ads elsewhere. Maybe that would allow facebook to recoup something like enough money to make it worthwhile?
(Oh, and guys, those marks are called diacritics. And FWIW, I thought, from looking at it, that it was pronounced stra-teach-ery, which now sounds even better to me, knowing that Thompson was an English teacher at one point.)