Whose Content Is It? (Yours if you want to claim it)
For me, the fundamental difference between a blog and a forum is about who controls the content. In a forum, you are posting data on a third party site (forum) which is about a certain subject, and the site host controls the data. It is less about YOU than about that subject - you are one of many quasi-anonymous participants generating value for the forum (and the site host). With a blog, you are writing on YOUR site, about various subjects, and all of your writings are yours. You are at the center of the interaction about those subjects. At the same time, blogs can emulate the functionality of forums in a less structured way with links, comments and track-backs.
On the other hand, blogs require active participation, and are (at least psychologically) harder to set up and run. And this may explain why sites like thefacebook, which are easy to set up and can be run with minimal participation, are so popular among college students (ie as opposed to them setting up their own blogs.)From a monetization perspective, to further comment on Umair’s question on property rights: on the web today, people can claim their property rights by becoming active participants and controlling their content. As per Anil Dash, a passive flickr participant can leave money on the table (sic) for flickr when people go to see his photos at flickr.com, but an active participant can have her flickr photos posted on her web site and claim the related ad revenues.