FRB is easy to create with Bitcoins... PrintCoins described the scenario rather well with his Mt. Gox example.

If you have a Bitcoin bank, (I believe this will happen for security reasons, as well as for facilitating other services,) then if that bank loans off a part of their reserves while still holding accounts (debts) to its depositors, then they're engaging in FRB.

I'm actually a big fan of that idea, because in that case such a bank would have a market competing with it for the same services, and a very valuable piece of information to use for choosing between banks will be its reserve rates. If the bank is set up correctly, its reserve rate can be well known by utilizing "green" addresses (well known addresses) for all deposits and withdrawals, as well as storage.

In such a scenario, the reserve rate can be calculated by looking at deposits to the deposit address, transfers to and from the storage address (probably held in cold storage,) and withdrawals from a withdrawal address to find the bank's liabilities and on-hand reserves. A fourth address could be used as a gateway within the bank for managing loans (with each account being a separate address known only to the bank and borrower,) whereas transfers to and from anything but the storage, deposit, or withdrawal accounts would be the bank's loan assets.

Given that address construction, all you need to do then is to calculate liabilities (what's held on account,) and weigh it against the calculated reserves to find the reserve rate, then you can also check that against the loans that you can also calculate from the loan address. Using this full system, the bank's average interest rates are known publicly, both for loans and deposits, in addition to having a publicly known reserve rate.

That would be an extremely good financial institution for an economy to have.