You said it yourself – you just don't get it, so perhaps it's not for you.
AFM, I couldn't be ar5ed with FB until a year or so ago – now I keep in touch with people I've haven't seen/met in ages. Twitter is brilliant for keeping tabs on what's happening in any field of interest – I use it mainly for work-related stuff, plus I get to contribute and share thoughts and articles, etc. Loads of other networks/apps out there – some good, some not so good.
One thing I can't fathom is how some people seem to be constantly tweeting or blogging, and yet still get a load of work done. How do they find the time?
Also, Twitter has it's share of people that post mundane b0ll0x – but all you have to do is unfollow them – simples.