It is hard to tell unless someone says so themselves. Perhaps some could post here if they want.

We know a whole lot came over here before and after grid.org closed.

Since this is part of BOINC many will see this on the BOINC project list, advertisement or statistics sites and come over here.

A referral question in the sign up process would give WCG an idea where new crunchers come from.

With this information a more productive solicitation could be attempted for new members.

I wrote a little about this earlier: http://www.worldcommunitygrid.org/forums/wcg/viewthread?thread=5500#44878

Since I wrote that, my team has slowly grown into one of the top ten teams at WCG - so I think the method works :-D

Expect things to move slowly. But if you can recruit just one member a day, soon you will have hundreds. If you can only manage one a week, you will still have 50+ at the end of a year. Once you get some momentum going, other people will help out and it will get easier.

I was introduced to the WCG at another forum I visit. The site administrator started a team, made a post explaining what WCG was all about and invited all the members of the forum to join.

I think the key to this type of recruitment is that it was done by the site admin who holds the most credebility. A random member doing such a thing may be considered SPAM. So if you are a member of a forum you think might be interested in joining WCG, talk to the administrator and see if you can convince him or her to create a team and invite members to join.