Twitter can be a great source of traffic and may be weak on producing direct income through adsense. But there are many upsides to using Twitter.
First and foremost is using Twitter as it was intended to be used. To come together with those of similar interests building a social network of your own while tapping into the network of your followers.
Doing this successfully your network expands quite rapidly as you tap in the network of new followers. The cycle continues.
Secondly is the direct contact you can have with people of the same industry. We are talking about other site owners, bloggers, business owners, media, etc.
This is extremely valuable for helping you to build authority. You tweet with those of authority so shall you become. With authority you build a much stronger visitor base who is easier to sell to and brand.
Thirdly comes a natural SEO aspect. Yes by building a strong base and becoming buddy buddy with other authority figures you will find that they begin to link to your content within their own sites. The better your stuff the better your chances. With those extra natural links your rankings will zoom in search engines thus bringing in more clicking visitors.
Part time bloggers will do the same. Also being able to get featured in media sources such as magazines, newspapers, and other print publications is a nice bonus.
Again use Twitter as intended. There isn't really any other media that has that many freely accessible users at the same time being able to directly communicate with those users. It is a pretty good deal just have to find what works best for you.
[edited by: arubicus at 10:11 pm (utc) on Feb 24, 2010]