I personally have not used facebook or twitter. I have a friend that swears by them, well at least twitter. I still have not found either facebook or twitter useful for myself.
I have tried and found the rss feed stuff to have potential as I can watch it in my sidebar and see when new interesting things pop up in the various sections of a sites I like to follow. But for the most part I just check my email for updates on specific threads I am following.
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, 1675