Greg Reinacker explains the skinny on how NewsGator subscriber (and NetNewsWire, FeedDemon, NewsGator Inbox, and NewsGator Go!) counts are reported. Basically saying that if you sync your newsreaders then your subscriber count is reported to FeedBurner as one person using NewsGator online.
Before this I tought that individual apps were pinging in addition to the NewsGator online count, and therefore skewing the actual numbers; but that’s not true.
For example, yesterday my FeedBurner stats report 445 subscribers use NetNewsWire and 739 use NewsGator Online. According to Greg, there is no overlap of users in those numbers; 445 subscribers only use NNW on one computer and 739 use more than one computer with syncing turned on. Of course, you always have to take subscriber numbers with a grain of salt. It would be easy for someone with more than one mac to not have syncing turned on, thus counting as two subscribers when they’re actually just one.