Personally in my case i started using Twitter close to 3 months back. Initially I was not sure how to use it & didn't see much value in it. However over the last couple of months I've really started to love twitter. The key is picking the right set of people to follow and start interacting regularly with your network. Quantity doesn't matter, quality does else you will get overwhelmed with junk.
Twitter has helped me build a good social network and interact with them in a meaningful way in addition to increasing the quality of my browsing time. One word of caution of using Twitter though, it can be pretty addictive and will eat away your time if you don't do good time management. Here again you don't need to browse all tweets, instead pick the tweets you want to read & respond back. If you try to read everything that comes your way it will overwhelm you. You might also want to use tools like tweetdeck, twhirl etc to organize and browse your tweets.
Here's another good video about Twitter.
Twitter in Plain English from leelefever on Vimeo.
For those who are in Twitter you can follow me - @Shogun1947. For those who are not yet in Twitter you might want to get started quickly and start building your social network!