I got a replacement L920 this weekend, because my first had some serious issues. Was able to reinstall WhatsApp on Saturday morning around 6am German time, without problems. One hour later, I was browsing the WhatsApp website and clicked the link to the WP app, and I got the message that it wasn't available for my device. Tried through the marketplace, wasn't there anymore to be found.
Boy was I happy that I somehow managed to install it before it got pulled. I have friends and family all over the world and it's my main way to communicate quickly with everyone.
I'd love it if it gets upgraded to be more integrated in the OS. Maybe even into the messaging hub as an account. It's functional, but a bit clumsy still. Don't have all problems many speak about though, generally happy with it.