Biggest disadvantage of Bitcoin for me is rates are still very volatile. and has no legal force.
But for online payments, bitcoin be one solution. besides perfectmoney, paypal or others.
i do not think that there is any big disadvantage of bitcoin. to me the only problem is that the transaction time is too long. some time when there is huge traffic, then the transaction take a lot of time which some time create panic like situation, hope that this problem will be solve very soon.
yes that is right that there is no disadvantage of bitcoin, and the transaction timing is a technical problem that can be solve, but i think this problem must be solve in priority basis. as it is really creating problems for the people.