One such service, Katango, says it has figured out a way to automate the whole process.
Katango, which has been available as a free iPhone app since July, launched a Web version on Wednesday. The service sorts your Facebook friends into groups based on a formula developed by Stanford computer science professor Yoav Shoham and graduate students there.
Shoham, Katango's co-founder and chairman, said the company wants to do for your social experience online what Google's search formula did for Web pages - organize them based on a useful and accurate algorithm.
Katango works even if you haven't filled out your profile with information such as where you went to school or where you work. Its friend-grouping formula takes into account details such as which of your friends are commonly tagged in the same photos, comment on one another's posts, attend similar events and so on.
In addition to Facebook friends, Katango users can also pull in their email contacts and add them to groups.
Of course, Facebook already lets users sort friends into separate groups. And Google Plus, the online search leader's most ambitious social-networking venture yet, was built on the idea that people want to share different things with different people online. One of its main features is "circles," which lets users sort friends, family and acquaintances into separate groups and share things only with them.
Still, Shoham believes the practice is cumbersome, and many people don't get around to doing it. Instead, they end up sharing too much with too many so-called "friends," or they clam up and censor what they post.
Katango's results are not always completely accurate, but Shoham says usually "almost every group makes sense." Users can make adjustments manually as needed.
"We tend to overshoot and over-include because it's easier to cross people out," Shoham said.
Katango does not show ads, and it does not yet have a way to make money. It is funded by "sFund," an initiative launched last year by the venture capital firm Kleiner Perkins Caufield & Byers to help social apps and services grow.