Poor people cannot currently rely on bitcoin
“The effort to make sure your bitcoin provider isn’t going to lose your money and your understanding of the volatility of bitcoin — I’d hardly say that it’s ready for, you know, poor people to have it go up and down by a factor of two and, you know — ‘Oops, I was at Mt. Gox. Now that’s not good. Now I’m at Bit-whatever.’”
Lack of transaction reversals
“So that basic technology shows that digital can do these things very cheaply, and the fees that have been building up over time won’t stand up even for small transactions. Now making sure that the thing is fraud-resistant and that money can be refunded – there’s somebody that you call up if you think you transferred to the wrong account or your account balance is not what you’d expect.”
Potential Anonymity
“Also governments, for most transactions, will want attribution, that is, the idea of a system where you can’t see — is that drug money, is it terrorist money? Should that be taxed? You’re going to have some tension between the attributed systems like credit card [or] debit card systems where there’s actually a record of who’s engaging and the purely anonymous ones. The one where I see it getting to critical mass, along with the government regulatory support we need is where it’s attributed; where we can see who actually did this transaction.”
http://insidebitcoins.com/news/bill-gates-3-criticisms-of-bitcoinThe last one isn't a problem for me but the first two are. The bigger problem is having no incentive to adopt BTC for ordinary people.
