Which Bitcoin weakness most hinder Bitcoins ability to gain market and mind share? Bitcoin has a few weaknesses. Among the well known ones are:


Transactions are not instantaneous.
Large numbers of transactions would bloat blocks.
Transaction fees are needed in some cases.
The client is difficult to use and its operation difficult to understand.
Wallets are difficult to secure. Coins can easily be lost.
Transactions are only somewhat anonymous.
Irreversible transactions are sometimes not what people want.


Of these weaknesses (including any I didn't mention), which are probably most seriously affecting the adoption of Bitcoins, both short-term and long-term?
If the credit card industry has taught us anything it's that merchants will accept whatever form of payment there is adequate demand for. Merchants have been perfectly willing to absorb some percent of loss from credit card chargebacks, bounced checks etc. for quite some time and will likely accept some percent of loss from 0/unconfirmed transactions (once we actually know what percent loss that is, anyway).

The real "sell" is with consumers. If enough consumers use bitcoins, merchants will begin accepting them - and even if they don't they still hold value as a means of long-distance funds transfer and perhaps as a store of value. Consumers also don't care about technical limitations, that's for us geeks to figure out on their behalf, so points 2, 5 and 6 are basically "our problems" to fix. What consumers will care about most, in my opinion, is #4: "The client is difficult to use and its operation difficult to understand."

When there's "an app for that" that just works and doesn't need whitepapers, wikis etc. to comprehend, the biggest hurdle has been jumped.