Nobody thought it strange he never paid down the principal?
Nobody throght it strainge his funding requirements never changed?
1 and 3 are the big warning signs for me. Why a single, uncapped fund? Unless he could place the ever-increasing amount of BTC in his fund at 10% every single week and the interest he was receiving was being compounded, his scheme couldn't be sustained. But if the demand was predictable, then why weren't the loans fixed term (even if that term was short)? How was he protecting himself against a sudden decrease in demand or against someone else offering his clients a similar service for less? How was he hedging his risk? Were his clients repaying interest only? If so, when was the principal due to be returned? What allowance had he made for his clients defaulting? Why wasn't he trying to entice the hoarders who are still sitting on large amount of BTC which barely ever move?
These are all questions to be asked the next time a similar scheme comes along - and it will.
I do think there are circumstances under which people will both buy and borrow at a premium, but when that appears to be happening on a large scale I think it's probably wise to curb one's enthusiasm and ask some difficult questions before assuming you've discovered the goose which lays the golden egg.
The theory that I've always thought for this is:
There are 50*6*24=7200 new btc per day. If pirate wanted to control the market price, he'd need to control a certain percentage of the market. The open deposit policy was a way to suck up those new btc. Obviously he had to continue to expand things to cover for that, but that is probably part of the reason 1) he was lowering rates a bit (even if people argue he really wasn't) and 2) he said he didn't know how long it would go on. Anyone that thought that 7% would continue for years is sadly mistaken. When I see the exponential formulas that people want to throw around and they're extrapolated to anything more than 18 months, I just write them off as trolling.
Do you really think there is a never ending line of rich fools out there lining up to buy bitcoins at over inflated prices week after week? Further,by compounding the interest they would need to increase their appetite for btc or he would need to find increasingly more and more rich fools.