Re: I have a bad feeling about this...
I don't know... a unit of a digital currency is a Unique Identifier. With Bitcoins these are mined, but a central bank could just assign them out, 1, 2, 3 etc. All they need is a record of who possesses which ID (like Bitcoin but I assume not exploitable by a 51% power possessing member, ahem) and an API for transferring these. We could stamp pound coins with a GUID and try it ourselves perhaps.
Flaws? A man-in-the-middle attack on the connection between bank and customer could be easily done you would think. Hack the server, all your 'Ecu's are belong to us? Blackout really cripples economy?
So I guess the important question is will be a "Digital Currency" ( a true currency controlled and underwritten by the central bank but paper-/coin-less in some way ) or a "Digital Commodity" like Bitcoin ( a scarce and hard to create mathematical construct with a finite limit that can be directly traded but with no underwriting ).