For me, twitter is an entertaining news tool, and a challenging game.
First, I would like to say, using twitter to market yourself is hard. I first started using twitter about a year ago, because someone at work suggested it was a good way to help market the company. At first, I found it rather useless and uninteresting, but after discovering the search feature, and then adding a search column to tweetdeck, I became a frequent user of twitter.
I started off posting some random thoughts, and trying to gather followers. Coming up with things to tweet was challenging and tedious. When you post a tweet, the only way anyone sees it is if a) they see it in a search, or b) they follow you. No one randomly follows you, and so you can't rely on you're posts being seen by your followers when you're starting out. So the first part of the game is getting noticed.
Getting noticed by having someone see your post in a search is extremely difficult. You only have a small window of time (often just a few minutes, sometimes only seconds!) before your post is so far down the list that no one will look at it. Second, even if someone sees your post, it has to be incredibly interesting to them, because they're getting posts from tons of other people about the same topic (and if not, then the search itself is unpopular).
Another way to get people to notice you is to include them in a mention (e.g., "you are so right, @wr_tomas!"). When you mention someone, they usually get notified, and if what you said is of any interest to them, they might follow you. The challenge then becomes keeping their interest.
I decided the best way to get and keep people's interest was to tweet about things I do at work, but also throw in some random tweets about other things that were on my mind every now and then. Unfortunately, I this hasn't really worked out for me, and it's hard to keep it up, especially if I get very busy.
But there's another side to twitter, and that's viewing instead of posting. Viewing is not at all challenging, but I do find it valuable. Following topics that are of interest to me (sharepoint, leadership), is very entertaining. I'm getting news and a lot of fresh, informative articles. Also, I think it's useful to know what is being said about sharepoint, because I work on sharepoint at work, and so I can be aware of common uses, frustrations, tools, and conventions.
So that's what I think about twitter. I enjoy the challenge of trying to gather followers, and getting fresh news from experts and fellow devs. You should definitely try it out – maybe you'll totally hate it, or maybe you'll become a twitter rock star!