also:
I agree that TF offers a very good service with interest on deposits and CDs. I use it myself.
By offering a fixed yield with repayment of both principal and interest throughout the life of the loan I am testing the waters - if you'll pardon the pun - for liquidity. Some amount of low-interest leverage is extremely useful when attempting to spread risk across multiple volatile assets - likewise if the repayment schedule and transparent security of backing assets is sufficient to create a supply of liquidty at a lower interest rate than the slightly more opaque system TF offers - all the better. It means people don't have to trust me (as the securing assets are locked up) - and depending on how much I trust TF I can profit from the interest spread should it exist.
The markets are moving fast, and the ability to leverage held positions rather than liquidate them to capture gains in other securities is a necessary tool for effective asset management.