Traders and speculators love it. MtGox loves it too. Imagine how much they made in trading fees over the last few hours.
Everyone else should hate it. A 30% crash and bounce back within a matter of hours? Not good at all for anyone looking to seriously use bitcoin to run their business...
Let's not forget that 'real' businesses also increase market depth and provide diverse arbitrage opportunities.
BTC/USD exchange rate price spikes up?
-Keep the price of your merchandise somewhat "sticky" instead of tying it to the dollar. Call it a "sale" and dump extra profits onto the exchanges.
BTC price tumbles on one particular exchange?
-Restock cheaply, if possible.
-Call it a "sale" even though you've been forced to increase the sticker price (maybe keep it somewhat sticky to stay competitive). When customers are enticed by the sale prices, what do they do have to do? -- Obtain more coins!
Thus I think it's a "chicken and egg" situation. If there were more businesses, they would drive down BTC volatility.