When I logged into 23andMe last night and went to Relative Finder I had 506 matches. I sent sharing invitations to 5 of the new matches and I sent a separate invitation to a Public Profile match. The remaining match was from someone with multiple people on his profile.
People who appear in Relative Finder share at least 7.5cM of genetic data with you in one location. Once you agree to compare your genome in Ancestry Labs, Family Inheritance: Advanced you may find that you share segments between 5 and 7.5 cM. The matching in Relative Finder occurs automatically for everyone in the 23andMe database. Of course, each person can opt out of Relative Finder.
Ancestry Finder uses the lower 5 cM cutoff and can match you with people who would not automatically appear on Relative Finder IF the person has filled out the optional "Where are you from" survey. The survey asks for location information on you, your parents and your grandparents. This data is used to show where the grandparents of people who match you in Ancestry Finder were born. There are a number of limitations to this data: current country names are used which may not really reflect the ancestry/ethnicity of the match; the data is only as good as the information the person completing the survey knows; just because a match has grandparents from X country it does not mean you do.
Both Relative Finder and Ancestry Finder should be used to research your ancestry. At this time Ancestry Finder is more difficult to use and it is hoped it will be come more like Relative Finder or be merged with it to make it easier to use.
The provision for Public Profiles in both systems has made it easier to determine if some matches might be more useful that others. It also provides the opportunity for committed genetic genealogists to let others know they are willing to share data.