On: Why did Skype succeed and Joost fail?

All I remember about an early Joost was the bizarre, grossly non-native GUI that was enough to make me bin the app after a few days.

Snap, I thought Joost's GUI was like an SDL (Simple Directmedia Layer) experiment gone horribly wrong. It was verging on Gibson cyberspace, but more likely, a kind of useless Minority Report interface.

I think you hit the problem on the head. Skype thrived on its simple user experience, while Joost's overcomplicated and kludgy UX killed it.

I can't remember how early on I tried it, but on my Mac it was incredibly unstable.