I like Twitter. I find it fun and the short attention span it requires suits me down to the ground. I have interesting and fun interactions with other people, many of whom are writer-ly types and it does rather make you feel as if you are not totally on your own after spending hours writing/researching/making notes, etc. You can just drop in, say hello, see what's going on, then come back out again.
What I don't like is being bombarded with messages to buy someone's book all the time! Tip: This isn't fun, it's not interesting, it's not polite and mostly, it's just annoying. It is also the surest way to get me to unfollow you, or not follow you at all, if I look at your tweets and see that this is all you do.
Someone put it well the other day when there was obviously a bit of a blast of this sort of behaviour going on, when she said 'Twitter this morning feels like walking through a market with all the stall holders shouting at you to buy something'.
As I say, I do like a bit of Twitter. It keeps me amused when I'm in a queue and can often give me a giggle when I'm least expecting it (like on a train whilst sat on my own yesterday...a little awkward!) and I like that. I don't like those who use it for ranting and vitriolic messages to people - whether they are well known or not. If you don't like someone, ignore them. There's no need to be nasty for the sake of it.
And by all means, feel free to mention your blog post - but not ten times a day! And feel free to let us know you have a book out - again, not ten times a day though. All this does is irritate us and make us less likely to even take a look at it, whereas a gentle hint occasionally can have the opposite effect entirely.
So, if you don't partake, you may want to give it a try. But if you do, be yourself and only let the salesman out every so often. It's much more fun that way!