I just read about Google's Sidewiki and after watching the short demo video, I think this is awesome. Many other services have come along to try to do this, including some firefox extensions but with Google's huge userbase, I think this will be the winner. yeah I can see comments about a website on StumbleUpon, but thats only a handful of people, really, and from those people only a few take the time to actually leave something useful on a site.
In short, Google Sidewiki allows you to enhance, or add useful information to *any* webpage. Check out the video:
I see one downside to this, as a blogger. Does it now mean that people will leave comments and feedback in google sidewiki instead of in my own comment system? Maybe its our job as bloggers to comment back in the sidewiki and encourage in-blog discussions for others --without google sidewiki-- to see and participate.
Yeay! I love technology, and think about what this will do for Social Media.