Today I found out that a wiki I like (but I don't edit) had started
being spammed, from its WikiApiary page: the exponential growth of
registered users, but not of active users, was suspect; a look to
RecentChanges immediately confirmed that a couple days ago (one) captcha
on signup was probably won by the spambots.
For those who do MediaWiki consultancy or would like to start, I think
there is an opportunity. Few wiki sysadmins go ask help, but putting
together some select metrics you could create a page on WikiApiary
reporting the wikis whose parameters recently got unhealthy: then go
offer an audit and improvement of their antispam setup, before it gets
so spammed as to require disinfestation (cleanup) services.
Just an idea I throw to get it out my mind, ;-)