Mt. Gox is NOT the same as Bitcoin.
Again, forget Mt. Gox (wow did they fall over tonight) - I'm mean to say: Nobody 'normal' will feel safe investing in a currency that's so vulnerable to volatility..
For the record: I don't give a damn, I'm sticking with this for the long run, better or worse.
Depends on what you define as investing. Some users will probably use Bitcoin in short time frames without much exposure to currency risk. Gambling, for example. Such use will add more liquidity to the system in the long run.