I guess some of the problems will eventually be solved, like usability and security for the average joe, insured exchanges and custodians also already happening.
I can only think of regulation and fraud, that can really stifle bitcoin's adoption.
Yeah, I think usability is not too bad at the moment for average people it is just about them getting their head around how it works. THIngs like the address book to store friends addresses and how easy it is to see how many BTC you have.
I think the big problem is about them learning how bitcoin works and wanting to use it after they hear about it.