So the question of the day - at least on Twitter, is what should Facebook's stock symbol be when it goes public? POKE was suggested, but I am guessing something more boring like "FB".
Note that F is already taken by Ford. An interesting point of comparison, the expected market cap for Facebook is around $100 Billion, and for Ford: around $47 Billion.
Assuming a valuation similar to GOOG, and a PE of 20, Facebook would need to generate around $5 Billion of earnings per year to justify a $100 Billion market cap.