Nope, I cannot, but I did download sidewiki and posted my own comment here, on the Mudcat, and it is available, BUT, I think only to folks who are signed into a google account and have the google toolbar which I am not crazy about.

Howsomever...your question is answered on THIS PAGE wherein they say (my emphasis):

What if everyone, from a local expert to a renowned doctor, had an easy way of sharing their insights with you about any page on the web? What if you could add your own insights for others who are passing through?

Now you can. Today, we're launching Google Sidewiki, which allows you to contribute helpful information next to any webpage. Google Sidewiki appears as a browser sidebar, where you can read and write entries along the side of the page.

In developing Sidewiki, we wanted to make sure that you'll see the most relevant entries first. We worked hard from the beginning to figure out which ones should appear on top and how to best order them. So instead of displaying the most recent entries first, we rank Sidewiki entries using an algorithm that promotes the most useful, high-quality entries. It takes into account feedback from you and other users, previous entries made by the same author and many other signals we developed. If you're curious, you can read more on our Google Research Blog about the infrastructure we use for ranking all entries in real-time.

Nice to see they are going to rank them and try to keep out the riff-raff.