I used to mine bitcoins a few years ago, and traded on an...

I used to mine bitcoins a few years ago, and traded on an exchange to leverage the coins I made mining. Lost the lot in the Mt Gox raid! As I see it there are significant issues with Bitcoin that don't apply to physical assets or currency:

1. The ledger is already so large and unwieldy that it places an enormous burden or heavy constraints on on new adopters. You either have to wait days and use gigabytes of bandwidth to synch a new wallet, or sacrifice a significant level of security and use a hosted wallet.
2. The founder completely failed to anticipate the level of technological innovation that Bitcoin would generate in terms of sophisticated, dedicated computing power devoted to Bitcoin mining. The energy consumed and emissions produced are disproportionate and impossible to control or regulate.
3. The original concept of bitcoin mining was that anybody could contribute, and the large numbers of participants would help to protect the integrity of the blockchain. But with the capital and operating costs of ASICs blockchain integrity is in the hands of relatively few large operators. That's a risk.
4. Only a cold wallet is truly secure. But you can't spend your Bitcoins and keep your wallet cold. The moment you bring a wallet online you are exposed to attack so the only way to keep your funds safe is to transfer your balance immediately to a new cold wallet. That makes managing your Bitcoins very inconvenient and cumbersome.
5. There is no facility in the Bitcoin protocol to replace lost Bitcoins. Every crashed hard drive, lost memory stick, cold wallet with lost credentials, and dead wallet owner results in irretrievably lost bitcoins. So in fact far from a "fixed supply" Bitcoin represents a diminishing supply of currency.

I see these as significant barriers both to widespread adoption and long term continuation of Bitcoin.