Someone is going to have to explain where the interest is coming from?  Loans you say?  Why would I loan Bitcoins when due to the very deflationary nature advocated i'm likely to have to pay back more value than I borrowed?  Accepting borrowing for margin trading (great... just what bitcoin needs, short selling), what would i possibly need a Bitcoin loan for that couldnt be served by a conventional loan?  Therefore how is this a killer app?