365% interest...not sure how that could possible be sustainable...

It's 26% p.a. so not 1% per day. So less likely to be a Ponzi scheme?

This is the way I see it - please correct me if I'm wrong

If you read the how it works then your bitcoins are converted to USD and you receive the interest on the USD amount and then that is converted back to BTC to pay you out. I.e if the bitcoins price increased by more than 26% p.a. then you would lose out in USD terms. On the other hand if the BTC/USD price did not increase by more than 26% or even fell then you win. So the actual USD gain is 26% p.a. minus the BTC/USD gain p.a. Their example shows the BTC price falling which demonstrates that you receive more bitcoin 1.89 (from a 1 BTC investment) and a 26% p.a. increase in USD terms. If you do the maths where the BTC price rises to $200 over 12 months then you still get a 26% gain in USD terms but you get back .945 BTC.

(Clearly this gives DC Bitcoin Bank the option to actually trade BTC for profit which makes them financially more viable if they get the trading right!. I would like to see self regulation to prevent this)

This scheme is pretty much giving you a choice between keeping your BTC as an investment for capital gains against the USD or investing in DC Bitcoin Bank and betting that BTC/USD will not increase by more than 26% p.a. over the term you pick.

Only problem I have is that the website does not show the sort of information that I would normally expect to see for an investment institution and therefore demonstrate how they might pay you back if their investments went against them.