I think the biggest disadvantages of bitcoin right now is that there's not many merchant who accept bitcoin as a payment method. The other disadvantages is the transaction speed, the confirmation can take a lot of time sometimes.
how can you say that this is the disadvantage of bitcoin. i think bitcoin is still not so much mature it still need a good time to become more famous. i think it will still take some time when merchants will accept bitcoin and will do trade in bitcoin. the transaction problem will also be solved very soon.