Nick makes a good point about Facebook, it can be a business tool or a private tool with social benefits. If people who love Facebook see your business details, its added exposure for your business. Exposure for any business is a good thing. If anything, just by being on facebook, it says to like minded people that your business is living in 2012 in the modern day, and your business is up to date so to speak.
Socially, people love to communicate, and communication is both entertainment and educational. As long as it doesnt take over your life, its a reasonable thing.
Once upon a time, to socialise with family n friends u drove over n said hello. Today, with time being in short commodity, facebook etc is a efficient way to catch up n say hello. I dont use facebook, I am too busy with work and dont have a need for it at this stage. My wife, however, is an avid user and has many girlfriends who share pictures of the young kids etc etc. Facebook is like AP, take what u want from it and use what benefits you. Plenty of useful information on the web these days. Its amazing how much stuff u can learn with a few keystrokes. Google i would argue, with wiki, is more relevant for those not using facebook. 
as i stated on the first page it is a tool you must use if you are a business, not using facebook for your biz is like not having a webpage these days
