Dion Hinchcliffe explains (also check the accompanying illustration with the post):
Some people are primary participators and provide both raw information as well as enrichment. These are the folks that are making Web 2.0 an active, useful, and vibrant place the most. Consider these folks your Flickr picture uploaders, your del.icio.us bookmarkers, and Ning information mixers. Notice that all three of these activities are creating new information at different levels, either as original source or by adding on top of what came before.
Other folks are secondary participators and mostly consume information, though they may contribute occasional enrichment in the form of tagging, rankings, reviewing, etc. These folks are also an important and probably larger group of people than the primary participators. What these people do in the Web 2.0 space is valuable and should be encouraged too, though making them primary participators should be the goal and this is what Web 2.0 concepts encourage.
Lastly are users that merely passively consume things on the Web. This is no doubt the largest group of users on the Web and are predominate in Web 1.0 since they routinely have no mechanism by which to participate on the Web. Web 1.0 design concepts failed to strongly encourage involving its users and thus we are often left with the silent, one-way Web.