As long as you don't have significant money in it, it's no big problem, but say you had your savings in it or were paid a salary in it - at that point the volatility would be a nightmare and the prospect of a bubble seriously troubling (bubbles always burst badly, and frequently go through successive waves of euphoria before they do). That the price has returned to a new high does not mean it will stay that high.

To supplant other currencies bitcoin would have to deal with the volatility and perhaps more importantly the lack of regulation and verification - with the current setup and community that'll be a huge issue, and perhaps impossible. It'll be really interesting to follow the trajectory of bitcoin and similar currencies as they negotiate these problems but I don't trust them just yet.

I do think email is broken for precisely the same reason - it thrived in spite of its anonymous insecure nature, not because of it, they simply didn't think about having to verify identity at the start, which has led to all sorts of problems with phishing and spamming. A lack of verified identity is at the heart of both these systems and causes issues for both of them, so I think email is a great example of a system which has problems of abuse (spoofing, spamming, phishing, fraud) because of anonymity being allowed.