I'm the admin for the DOpus Resource site and I haven't seen any bot spammers at all since I changed two things in phpbb3. Firstly, only members can post, and secondly instead of a normal image captcha I am using a question captcha which asks a question regarding the authors of DOpus. This seems to have stopped them dead in their tracks. Of course, this won't stopped a real person from spamming but we've rarely seen that. In phpbb2 I used a mod called "Textual Confirmation" which does that same thing as the question captcha. Again, it solved the spam problem.
Whilst the stopspam site is a good idea, it slows down the registration process for new users and/or creates a lot of work to keep on top of the list.