A large problem with Wikipedia is that there are times when information it contains isn't accurate. There have been cases when it was something that was completely made up.
The information is provided by people who are anonymous and others who are anonymous can make changes to what has been provided.
Google is starting knol and will use authorities on subjects and the people will be identified. Ads will be allowed with knol and the authors will get what Google calls a "large share" of the ad revenue.
At the present time knol is in beta and is invitation only.
Very often Wikipedia ranks very high in a lot of search results. Google often makes changes in their algorithm. Some experts say that if Google increased the importance of links to an actual page rather than to a domain, Wikipedia wouldn't dominate the search results the way they now do. There is all types of speculation as to how that could help knol and hurt Wikipedia but it does involve a lot of speculation on the part of what Google may or may not do as well as what they may or may not do with knol.
Here is an example of a knol so you can see how it compares to Wikipedia
An example of a knol -- Insomnia
There are a lot more details to all of this and here are a few links to additional information.
ITworld.com - Blog Insights: Google Knol Battles Wikipedia
Google Creates Knol: Invites Users to Share Knowleddge
Why Wikipedia May Not Be Totally Safe From Google Knol | Altogether: Full Service Online & Digital Marketing Agency
» Google Knol: Wikipedia killer or knowledge management app? | Between the Lines | ZDNet.com