Granted, most people do not see Knol as a direct threat to Wikipedia, and the title of the post might upset some people… Even Google noted that Knol is not designed to compete with Wikipedia, but you have to admit that from a online knowledge-base perspective, the sites are quite similar. Knol might become the preferred choice in this field within a very short time.
1. Moderated data
The big difference between the two is that Knol is less anonymous then Wikipedia, it allows the author to moderate their respective articles. The idea is that the Author remains involved, since their name and reputation is permanently attached to it. This approach takes people out of anonymity and potential incorrect contributions, and might lead to higher quality articles prone to error. Knol allows the community to rank respective Knols, and allows more Knols about the same topic, another big difference between the two services.
2. Ads enabled
Knol will have ads enabled from launch, supplied by Google AdSense. Simply enable your adsense in your profile page, and you are ready to make some money from your content. If you have been contributing to Wikipedia (or not), simply copy your data to Knol and get Adsense dollars from it. (read more)