chautemoc: I used to hate Twitter, now I'm happily an addict. What I didn't understand and what many don't is it can be for whatever you want, not just banal "I'm doing this crap that nobody cares about" posts. If you follow a bunch of people with a similar mentality, it becomes very interesting and addictive. I don't visit most websites unless they use Twitter anymore...it's great as a news service.
More on topic, no, it's not essential for GOG by any means, but it sure is fun to interact with GOG and other users that way in addition to the forums, and also to spread the word.
Not really. Biggest problem with Twitter is that you cannot directly message someone, and they limit the room you can use.
Ideally, Twits would be better than Crackbook, since it's the essence of Crackbok distilled to a small package, but in practice, Twits tries too hard to be different, and thus you are better off just using FB and ignoring everything but the news feed.