There may be reasons to worry about the Federal balance sheet, but that chart is not one of them. That chart shows the amount that banks have borrowed from the Federal Reserve. What it shows is that, during the credit crisis, banks have been less willing to lend to each other, and hence they are borrowing from the Fed instead.
Put another way, those are Fed assets, not liabilities.
Capital Assistance Program: Convertible Preferred Stock with a Twist [View article]
The Scariest Chart Ever [View article]
Put another way, those are Fed assets, not liabilities.