I use it. I didn't find it easy to get the hang of it at first.
I only follow a few people permanently.
I think it is unlikely that anyone will get a message from some of the more popular Tweeters (although I knew somebody who got one from Stephen Fry.)
It is also possible to send personal messages which cannot be seen by anyone else.
Some people send Tweets which I cannot understand because I am not familiar with their group or their jargon or slang.
Others are great Tweeters.
Can be very useful for keeping up to date with a person or organization.

I joined just after it first started and used it quite a bit. Haven't done for ages, mind, but may start again.

I don't use it or facebook etc,well I have some games on facebook but that's it.

Couldnt work it out, seems to be where the celebs have their spat now though so i might have another try at some point just to be nosey

I don't have an account but I used their search feature for the student protest updates... and I like seeing what the (fictional) Queen tweets and the Archers' characters' "Twitters" are a laugh as well

Me and a couple of friends follow each other, but we don't log into Twitter regularly, so it's a waste of time really. Much easier to speak on the phone or text.
So it is mainly for following  famous people and celebrities of various kinds.
It's a self-publicity thing more than anything else.