Blogs and Wikis are two aspects of new media. To be honest I have limited knowledge and experience with Blogs and not really sure what the fuss is. I have however spent countless hours reading articles on wikipedia. I never really got involved with editing or collaborating on wiki. I just like reading articles there for the huge sources of information.
Which brings up the most noticeable difference between blogs and wikis are that for wikis they are supposed to be objective repositories of knowledge where anyone can edit the content. As this CNN article points out is that Wiki is often criticized for its inaccuracies so they are focusing on refining their articles with proper references and citations. It is essentially a form of many to many communication.
On the other hand, blogs are more about personal opinions and thoughts without any sort of filtering or regulation. It is primarily a one to many communication. Visitors can post comments but cannot edit any of the content. As far as I can tell blogs aren't as popular as wikis no doubt due to the collaborative communities found in wikis.
As more people gain high speed connections to the internet, the more important internet social networking becomes, and the more essential collaborative sites like wikis and blogs will be. Since blogs also allows people to easily communicate their thoughts and have others comment on them, they can also be used for collaboration. Blogs have more direction communication features compared to wikis. For wikis there aren't too many direct communication features. So that means bloggers can easily collaborate by adding each other on their blog lists and commenting on posts.
I am not creative enough to think of new uses for wikis. But I imagine if they could implement some direct communication features similar to blogs, it could allow for more closer knit collaboration. And even have a user section where you could post your own blogs. There is no reason why wiki can't incorporate social networking features into its site as a subsection.