(via Andrea Matwyshyn and Lilian Edwards). This is quite an ironic problem for an anti-spam site. The Anti-Spam Research Group (ASRG) of the Internet Research Task Force (IRTF) used to have a wiki, until it had to be shut down due to continuous abuse by spammers.
Yes, wikis are well-known vulnerable targets to spammers. This in itself poses many interesting questions about the viability of wikis. With the exhuberantly humongous success of Wikipedia, wikis have demonstrated that they have tremendous potential as a communication tool.