As of yet there is no native Skype app for the BlackBerry PlayBook, but there is a nice workaround that allows you to use Skype from your PlayBook by taking advantage of Adobe Flash v10.3 support in the browser. The same goes for using GTalk, Yahoo, MSN, and a few others as well. How does it work? Simply go to http://imo.im/ from your PlayBook's browser and then sign in to one of the many messaging application options.
I tried it myself, and the Skype calling works pretty good. The PlayBook's QNX microphone picked up the sound very well, and the speed was pretty fast, not much delay. Let us know if you give it a try, and how it works for you?