The biggest disadvantages of Bitcoins are can't be use in the actual store because bitcoin is intangible and bitcoin can be lost instantly in your wallet if the file corrupted.
i think it is not the disadvantage of bitcoin but i the main reason is the the user of bitcoin are still very low, therefore the facilities of bitcoin are not yet available everywhere, but hope that very soon we will be able to use bitcoin in our local store also just like fiat currency.