Congrats to the Kik team!
When I first heard of Kik, I thought it to be somewhat repetitive. There are tons of apps just like it. But, the viral nature of the app sold me. The fact that contacts are automatically added allow me to use the app immediately.
The next steps for Kik are crucial. People are going to have a problem with being so accessible to people they don't know. The ability to block users might arise conflict with "Why did you block me on Kik?" I'm interested to see how they handle these issues. On top of that, they're adding image support, which I think is a pretty hefty dent on their servers.
Again, congrats on the growth, but good luck with keeping your users! As of right now, it took me a whole minute to send a Kik message out. I'm sticking to Blackberry Messenger for now, which by the way is an amazing client minus lack of cross-mobile platform availability.