Sidewiki is available as part of the Google Toolbar and can be installed on Internet Explorer or Firefox. Curiously, Google does not have a compatible version for Chrome yet, but it will be available as part of Chrome.
Once installed, you need to log into Sidewiki with a Google account. You can go to any Web site or page and a side panel appears where you add your comments or your links. Google's intention for Sidewiki is to create a way to annotate Web pages with expert insight, additional background information or any other useful content that anyone can add.
So far, however, this isn't the way everyone is using it.
Looking at some of the comments on various Web sites, some people are using Sidewiki as a Twitter substitute, giving status updates about what they are currently up to. Sidewiki does have a feature that lets users vote "up" or "down" a comment, rating its usefulness -- this is in hopes that less significant commentary gets relegated to the bottom of the comment listing.
We tested Sidewiki on both Internet Explorer and Firefox. It worked on both but a couple of times Internet Explorer logged us out inexplicably from our Google account.
The first thing we thought of when testing is the potential for Sidewiki to be exploited by spam-bots and other ill-intentioned schemes. Although Google has a clear-cut policy prohibiting spam, malware, porn or abusive language, it's going to be interesting to see how Google manages this.
