I wouldn't put a site online without GeoIP blocking. If you are operating an English language site primarily for US citizens for example, why even allow access from countries that have no business on your site. At the very minimum, access to the join form should be restricted.

I have also used Maxmind's proxy detection service to block access to the join form via US based anonymous proxies. This is a paid service, but for mission critical applications, it's worthwhile.