As Hans said, we (well, I) really tried what we could... plugins, captcha, custom questions and whatnot.
But the number of spam accounts was just way to huge. We're talking ~600 accounts in one month
(that was the November last year, you'll still see it in the forum stats).
And I have better things to do than check all new users / delete 20 accounts per day

I'm open for any recommendations regarding forum software with better anti-spam utilities, as long
as migrating the data is not a pain in the behind, though
