http://news.cnet.com/8301-1023_3-9997426-93.html
It seems like the biggest difference is that there will be more public ownership of the articles written/edited for a Knol than a Wikipedia
entry.
I like Wikipedia but always take things posted there with a grain of salt. I'm not sure if my faith in what's read on the internet will change all that much, even with author ownership, but I'm curious to see how well Knol does.
Google seems to have its hand in just about everything, but so far, I love everything that Google has been a part of (I doubt that I will ever stray from gmail, for example).