Its very very simple – facebook is a closed community of friends. Twitter is a massive data stream open for everyone to explore.
Facebook can’t do hash tags, and even if it could, the accessible data set would be so tiny it would be stupidly useless.
So after weeks of trying to enjoy the new facebook 3.0 layout, giving it a chance like I did the facebook 2.0 layout (and ended up loving 2.0) – facebook 3.0 is a big flop for me.
But huge props facebook for trying to improve the experience continually.