It is sort of a AGN user rating system. The more "accuracy" a member has, the more members have hit that little plus sign and made a favorable comment about/to that member.
That is not to say that a member with a lower accuracy rating is less reputable, reliable or trustworthy!
Accuracy just denotes, for the most part, how helpful a member has been based on the number of people who have upped that member's accuracy rating by clicking and making a short comment about that particular interaction.
In general, an AGN member with a high accuracy rating is probably a helpful, knowledgeable person and most likely trustworthy... OR NOT!
Useless for the most part because it doesn't allow negative feedback.
I think... LOL!