Keith,
I'm not sure what you mean, or if you're posting in the wrong topic. Above your post, there wasn't a discussion for showing the JFBCContent plugin based on users, only by specific articles.
As for what I think you're talking about (the status message updates on login/registration), we don't have any method right now to limit or prevent the messages. I added a task to our tracker to check what the last status message is on Facebook, and if ours will be the same, don't post it. Facebook already prevents duplicate messages, but we've seen them get through here and there.. so our check can help. As for limiting it to once a day or by user, that gets tedious as we'd have to have another database column to track the last time we posted, and gets crazy if other extensions are trying to post their own updates, so we won't be implementing that any time soon.
We'd suggest just turning off the login message for now for your purposes. You can leave the registration message on though, as that shouldn't show up multiple times.
Hope this helps, and thanks for the ideas and feedback.