all mail to haskell.org goes through the Yale spam filters, which aren't that good. Most of the mailing lists on haskell.org are set to hold all postings from non-members for moderation, which catches 99.99% of the spam. Some lists are set to reject outright any non-member postings (ghc-users, for example, because my life is too short to spend wading through another 50 spams every day).
the trigger for my question was that I seem to receive almost no spam via the other haskell.org lists, while there is the occasional one via hopengl. It hadn't bothered me too much, but in a recent exchange I refered people to the hopengl archives, and having spam in the archives is annoying, esp given the level of normal traffic. See march or december for extreme examples. cheers, claus