Having joined both these social media sites just after Christmas it's been interesting to compare the way they both work and, for me anyway, Twitter doesn't.
The 140 character limit is very restrictive in terms of actually getting to know people and really it's just an advertising site. If you approach like that then you won't be disappointed... but I suppose I was expecting a bit more.
Here on goodreads you can actually converse at some length about all sorts of things- not just books- and the key is joining groups and getting to know a few people.