While I do not personally enjoy Facebook that much (I see a lot of my friends over-using it with pictures of hamsters, etc) I do see its value as a way to keep in touch with people.
I wish they would limit the amount of use some people get so I wouldn't face so many trivial messages every time I log in.
But I do have a real dislike for Twitter - I don't think they are anything alike. I see the value of Twitter as a resource for people of like minds to communicate on a quick basis, but in terms of comparing Facebook to Twitter, I don't think there is any comparison. Twitter is for "right now" chats, but not for reading news. etc. Therefore yo have look very closely at who you reach with a twitter strategy (for businesses)
1) you have to be logged in to Twitter to see the tweets of people you subscribe to - especially now that they have thrown ads into the mix. With Facebook you can log in and see just the post of people you care about, but more importantly they stay online forever, and they are not limited in text.
2) Twitter is nothing more than AOL chat rooms updated to carry fewer characters. Remember how popular those chatrooms used to be? And look at them now. There is a cruise chat on Twitter once a week and the last few times I tried it it was inundated with spammers and web bullies coming in and leaving obscene messages ,etc.
3) Twitter says their "average" user only visits 2.2 times per month. I'm sorry, but that is a very telling and horrible metric. That shows that "average people" - consumers, potential customers, end users, are NOT using it.
The fallacy of Twitter is that companies believe they are reaching potential customers. For example, many of the cruise lines have been sponsoring "Twitter" cruises lately - but who reads them? Mostly only other cruise professionals - certainly not many casual travelers who may be considering a cruise int the future.
NCL started out with an aggressive Twitter approach several years ago - but they dropped it after 6 months, I believe because they saw it just was not worth the effort. But other cruise lines have now picked up the ball and are running on Twitter, and I really just don't believe they are getting the reach or ROI they are expecting. Why do I say that? average visitor, 2.2 times per month.