Fred Wilson has a post, Twitter.com vs. The Twitter Ecosystem, that is an essential read for anyone whose job involves Twitter.  Strike that: it's important for anyone in business, period.  I say that because the evolution of Twitter and similar "sharing" services is happening much faster than many people realize and it is reflected in the numbers that Fred shares.  Anyone in business will be directly affected by that trend.

Please read Fred's post for yourself and keep in mind that his audience is a geek-ish, early adopter crowd, but over the five years I've been reading Fred's blog I've found them to be highly predictive of the world of communication and commerce that is about a year down the road. In other words they are behaving now the way the average consumer will be behaving in the next year or two.