In some ways, Twiiter should be more straightforward vis-a-vis valuation. It basically has one product. FB is expanding into quite a bit more diverse territory. Plus, Instagram could be a big deal for them and is basically not being monetized right now.
Jay it looks like Twitter have taken note of some of the criticism following the FB IPO. Interesting to see the level of volatility in the FB stock price given the size (mkt cap) of the business. I think it demonstrates that the market still is unsure on the true value of these companies.