What's causing the volatility and weakness?

The main driving force for this weakness is interest rates. An easy way to see this is to look at the iShares Lehman 20-year Treasury Fund ETF (TLT:AMEX), which has fallen sharply for four days now and is approaching levels we saw in November. In some respects this is a positive, because it indirectly accomplishes what the Fed said it plans to do by raising interest rates.