We post a note on the board every so often about the benefits of registering, etc. This works fairly well and those not registered have a tendency to actually read it. It then also gives them the opportunity to ask questions should they be concerned about registering for any reason.
We have also found that this will occassionally get those that have registered but still not figured out how to log on (I know it is difficult []/testimages/icons/crazy.gif[/]) to be able to ask how to do something on the boards.
