it is important just as other social media such as ezine or digg. But it is not as important as search engine
I've found it very useful. My directory submissions have exploded and when I update on a relevant topic/post/article within my niche, within seconds I've got immediate traffic. I keep my followers/followings within my niche as that's the people I like to communicate with to keep up to date in the industry as well as find useful tools, articles and information from Tweeple in helping me keep my sites optimized and performing.
I don't like it, really i ever don't know why. i used it for while buty no traffic from it. i hdon't like the new huge web like twitter, facebook...etc