1) The unstable Confirmation time (Kinda hard to be realized in a fixum of 10-minutes of 1-minute)
2) The unstable prize.. because its not widely accepted as Currency, more as a stock.. But BTC actually reacts like a currency on FIAT falls/rises
Bitcoin reacts on more than just fiat falls or rises. It basically goes up and down depending on what happens around the world. While that is awesome for traders (and for me, because it's always going to be unexpected), there are some bad things about it.. For example, if something like Bitfinex happens, Bitcoin is going down a lot, the mainstream media is writing all this stuff about Bitcoin and people will be afraid to ever invest in it...