I disagree, none of my friends use WhatsApp and I've never heard them mention it. It's all about group texts or FB chat groups. (I am 23)
Facebook really should create a whatsapp for System 30+ -- they would dominate that market.
Whatsapp is really important in some markets. Just because you don't know anyone using it doesn't make that less true.
(Also, I use it, so now you do know someone using it!)
Also understand that I am FULLY aware that I do not represent my age group nor do I represent even the "average" "young" person. I represent a small demographic but I wanted to give my views from that position.
I'm just saying, just because people with dumbphones or feature phones are clamoring for WhatsApp doesn't mean that people with smartphones care at all about the service.