Just because the application has huge flaws from a certain developers perspective doesn't mean other people will share the same view.
I use whatsapp regulary along with my team to coordinate driver & share info/media quickly to allow the driver to do his/her job and vice versa. Having a desktop client is a god send for this as switching between computer/phone gets very tiresome.
It won't replace slack but it makes life a whole lot easier. Slack is a lot more business orientated and that definitely shows whereas WhatsApp has the convenience factor for people eg. driving and giving us real time info.
Why not? Twitter, Facebook, Google, and Amazon all use a lot of Java. It's come a long way since when Microsoft shipped rollover buttons via Java applets in MS FrontPage.
It is definitely a work in progress, but it feels pretty good to me. After having iPhones since the first one, ios7 is refreshing and a long time coming. I think I would have been ready to jump ship if ios7 had been another Forstall creation.