User comments have always been one measure of a website's search engine ranking, but it seems they may be about to become even more relevant, with Google's introduction of Sidewiki.

This lets visitors to every website read and comment on its content, with the comments being incorporated by Google in its algorithm to determine site rankings.

Sidewiki is a new Google Toolbar feature allows web users to read and comment on any and every web site. Users need IE6 or later, or Firefox 2 or later to be able to install the toolbar.

SearchEgnineWatch reports that, unlike blogs, the most recent comments won't appear first. Instead, Google is using - what else? - a ranking algorithm to place what it deems the most relevant comments first.

It adds that very few sites are so far adopting the Sidewiki, but observers are hoping that more relevant content will be added in time.

Google has posted this introductory video explaining how Sidewiki works, but the comments so far submitted to it seem mostly to express reservations about the potential for spammers to hijack the comments. So no doubt, many people will be reserving their judgments until more is known about how Google intends to address this.