Now known as just Xmarks (download), the tool layers in site discovery features. The Xmarks plug-in shows you sites similar to the one you're on, based on what other users have bookmarked and where they've filed those bookmarks. The plug-in also gives you additional information in search results, letting you see site popularity and user ratings on your search hits.
All roads also, optionally, point the user to the Xmarks site, which has more reviews of and data about sites, and wiki-like directory of sites.
Xmarks is used by about 1.5 million people, CEO James Joaquin told me, and it knows about 600 million bookmarks. That's a lot of data to mine, and I asked Joaquin if he thought about offering a StumbleUpon-like feature to help users find completely new sites. He said Xmarks' model is utility, not entertainment. His directed "more like this" discovery is closer to the original Foxmarks mission, he implied, than the random walk down the Web that makes up StumbleUpon.
What's not clear, yet, is how this handy new function makes any money for the company. Xmarks may be able to sell some ads on the Web site, but even Joaquin doesn't seem to think that will be an appreciable revenue stream. And the system's utility is primarily in the browser; I expect only a fraction of users will spend time on the site.
Xmarks still performs the function it was originally designed for: It capably synchronizes users' bookmarks across machines and browsers (Firefox, Internet Explorer, and Safari). The new features look like a nice bonus.
Foxmarks was started by Mitch Kapor, the founder of Lotus Development, to solve his personal frustration with bookmark sync. Kapor was also the founding chair of the Mozilla Foundation, which created Firefox.