I just got curious as to what is available on each store for the "connected" ones...
Here's a screen capture of the Apple AppStore, Google Play and the Blackberry World for the Playbook:
Facebook, Twitter, Skype, Google or LinkedIn are available for Apple and Google. That's a different story for Blackberry where only the official Facebook app is available and it looks like an old version. Other apps are basically launchers or third parties of bad quality... So if you think about being social on a Playbook, you'll have to rely on the web browser.
For the iPad and the Nexus 7, all that is required, is available. Apps have basically the same quality and the same features at 99% (Android Facebook lets you change your Cover picture for instance).
If you like mobiles apps, you won't be disappointed with the Nexus 7 or the iPad.