I think it's worth talking about at least. One concern I have is that it may drive away some people who might sign up otherwise. Let's say someone discovers Hubski on the second of the month, and is intrigued by the site. However, he doesn't know anybody already signed up, and subsuquently forgets about Hubski before the first of the month comes around again. Essentially my point is that restricted sign up times may drive away some folks who might otherwise become contributors. An idea I have is that, perhaps, there could be someway for folks to apply for membership at any time. This could be in addition to the invites and restricted open signups, or an application only policy. For example, an applicant could select a few articles and discussions that were recently posted, and write up a few brief thoughts on each one. I feel only someone who was serious about joining would go to such effort, and, potentially, community members could vote on submitted applications.