I like the concept, as a communication vehicle that is somewhere between a blog with comments enabled and a service like Twitter where people can comment on all kinds of subjects at the drop of a hat. Talk about giving users control! Of course they are at the same time taking control away from the webmaster, in a big way. I didn't see any way a webmaster could opt out in my quick glance.
For a search engine, which after all is Google's main business, it's a stroke of genius!
Forgetting about the benefits for real users for a moment, can you imagine how they could use such real world, hopefully thoughtful, user contributions to help them in figuring out what a page is actually about and what said real people think of it?
And they get the double whammy. If Sidewiki gets heavily adopted not only do they folks to tacitly agree to let Google track their every movement on the web (they have to know the page you're on to activate the tool after all) but for those who are actually commenting you'd have to be logged into a Google account, so they could easily build a database of your likes, dislikes, etc, leading to easier and greater personalization in the search realm.
Pure genius to give folks something that is cool and brings them data they can't possibly get any other way.
What I hate is that it requires one to install Google's toolbar, and of course the constant tracking that's got to be happening for it to work.
What I find funny as hell is that none of these cool little tools seem to work with their own Chrome browser, even though they hype how much better and faster Chrome is than other browsers out there.
You'd think someone would make sure that one was supported in the very first release of everything they pump out!
