Last month, Google announced 'Knol', a commercially sponsored wiki-type site. I have mixed feelings about this. Although I don't have anything against advertising-based content, I'm not sure how many editors will leave Wikipedia for the chance to cash in.
I'm personally a big fan of Wikipedia. I've been an editor for years now, and I've created some articles, started several more stubs, and enjoyed the community aspect. I'd hate to see it lose steam because the volunteer editors leave to make a few dollars with adsense.
On the other hand, I'm excited to see what Google's engineers can do with the wiki concept, and Wikipedia could even end up benefiting from the competition. Knol will have a blogger-type interface, Google's hardware, and I've heard it may have a digg-type social rating aspect. I'd love to see how these aspects work with the web encyclopedia concept.
In general, I love how the collaborative aspects of wiki's are becoming widespread in the business world. Wikipedia has a for profit corporate arm, Amazon has started a product wiki called Amapedia, and my team even tried out a distribution on a development server at work.
The difference is that Google's Knol isn't aiming to create a corporately-oriented wiki, it's competing directly with Wikipedia. The paradigm shift is that it will be monetizing itself with ad revenue instead of supporting itself with donations.