I have tried Twitter on and off, but now find myself logging in each day. Twitter has really "matured". Twitter should not be regarded, however, as only a tool to increase blog traffic.
Here are my top reasons for participating on Twitter, and why perhaps you should consider as well:
1) First and foremost, you can of course update your followers about what you are doing, reading, or blogging. This can help increase traffic to your blog. But don't expect tons of traffic unless what you are posting about is VERY timely.
2) Get updates from the best and brightest - many people are on Twitter. I follow the Best Buy chief marketing officer, William Shatner, Matt Cutts, to name a few. This is often a great source of new information as it happens. It's always on Twitter first.
3) Did I mention William Shatner is on Twitter?
4) Even if you are not seeing tons of clicks coming through from Twitter, if you participate just for what it is, you can meet tons of new people that will grow your network which in turn will impact on the success of your blog.
I have been really enjoying Twitter lately. I find I am more up to date now that I am following some key Twitterers, I have gained some traffic to my blog as well as some new subscribers.
Good luck!