The spam bots are 'successful' because so many boards have open posting policies. I run forums using the SMF code, and have not had any issues with bots making guest posts yet (knock wood) except in the guestbook area of the Lunabyte portal I use in conjunction with SMF. I fixed that by disabling the guestbook.
Registering on a board shouldn't be a big deal if you want to participate on the board. With anonymous email addresses like gmail, hotmail, yahoo etc, it's not difficult to maintain whatever level of anonomity which some people want.
So yeah, I'd be in favor of requiring registration before posting.
1979 Type 1 Convertible 1976 Scirocco (For Sale!)
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