As I see it there are several main uses for twitter.
– Friends can use it to organise events, keep in touch and see what others are up to.
– Companies can use it to cultivate a more enthusiastic group of customers. I would say that direct interaction with companies and organisations you are interested in is very powerful
– If you are just a nobody, you can follow interesting people (see my list of recommendations in the older thread). These sort of people usually have something interesting to say.
If you are still in doubt, just use The Goggle to search for “what is twitter” to see some articles about how different people are putting this simple tool to use.
-j
p.s. I fall squarely into the third category, but I do use twitter to update some embedded code on my website for status updates.