Xmarks CEO James Joaquin told me the Xmarks active user base is currently 4 million people, and that the company manages a database of more than one billion bookmarks consisting of 350 million URLs. Xmarks users conduct roughly half a billion searches per month.

The overlays (see image below) only appear to searchers with the Xmarks browser add-on (now available for all browsers) and not the rest of the search audience. And they only appear for advertisers that have subscribed to the service.

Here’s an example what Xmarks users might see in the right column of Google in a travel search result:

The ranking (#1) in the ad above is implicit and derived from the aggregate number of users who’ve bookmarked the site in the travel category, while the star ratings are explicit and based on users’ feedback on their bookmarked sites.

SearchBoost costs $29 per month; and in addition to the visual overlays there are analytics that come with the subscription, including data on organic CTRs and competitive data for both paid and organic search.
Joaquin told me that in early test with approximately 200,000 users SearchBoost improved CTRs on paid ads by 15 percent.

In general there’s a move toward branding in search, as well as incorporating more visual elements in paid search ads (e.g., Google image ads). This is broadly consistent with that movement.