I've been invited to the beta and while I've not had much time to experiment, it doesn't seem any more complex than any other application. Ordinary people manage to use apps like Photoshop or Microsoft Office yet their extremely complex (if you base complexity on features and learning curves). I think everyone gives the public too much credit in thinking they know more than they do but too little credit in assuming they don't know enough because their (lack of a better word) stupid.
Doubtful, it's not just some web 2.0 app, it's an entirely new protocol (literally), in the same way FTP, HTTP (et al) are protocols. While it certainly won't drive away the likes of email, it has it's place, a very good reason for being and I personally think it holds a lot of weight (when it's matured a little further) into becoming a very powerful collaboration tool that even the likes of Facebook could integrate. Remember that it's not some application (said twice for added impact), it's a system and protocol that can be embedded and used within any application, service or future communication method.