No idk, but 50'000 is an amazing number. But there would be much more download if it would be an official app. To us its very easy and self explaining to install Wazapp. But that's certainly not the case for everyone - many people just have a look at Nokia Store to check for new apps and wouldn't even think of that they could download an application from any website. Still see quiet a lot of people asking if there is "WhatsApp for N9"...