I think the only way bitcoin adoption can really grow at this point is only if BTC become useful for something. Nobody wants to invest on something such risky now.
Bitcoin is very useful. It serves the same kind of uses that paypal serves except that bitcoin does not rely on any central authority to keep track of users' balances (when you use paypal, the operators of paypal will keep track of your balance for you - and manipulate it if they choose to do so).