Most of those services seem to require some sort of information to create an account. My plan (for the BitCoin side anyway) is to have it be completely anonymous, no need for e-mail address or submitting even a username/password form.
I might be interested. Anonymity aside, if you can make it really fuss-free to get an account that'll be a real win.
I think the viability of such a venture depends largely on the marketing. Can you communicate the uniqueness
of your service effectively to a sufficiently large number of potential customers?