sem101 – I use two plugins that ask questions before signup
This prevents most of the bot sign ups that we plaguing us for some time with those group creators.
This does not stop the manual spam signups, so we have delete a few accounts each week, but it has prevented the tons that we were dealing with before.
We used to have good luck with /bp-registration-options/
but we started having some issues around bp1.7 I think. Other people say it works now (https://buddypress.org/support/topic/feature-request-new-user-moderation/ ) – but I don’t have time to play with half baked / half working solutions. Your experience with it may be fine.
We do not use si captcha any longer as we had issues with some multisite problems. I do think it slowed down some of the spammers, and certainly cost them time and a little money to get around it – so it’s cool.
I use one of the blog defaults type plugins to auto set new blogs/(sites) to have settings like ‘users must be logged in to comment’ – and “discourage search engines from indexing” – this has helped a bunch for us.
Of course the manual spammers will still need to be manually deleted – you will never stop the manual spammers, if you did, then you would stop regular people from signing up. Unless of course you went for one of those “invite only” buddypress setups.
I recently donated to a plugin author to create a new plugin that allows superadmins to force certain settings on sub-site/sub-blog users.. like forcing only allowing registered / logged in users to comment. That plugin is working, but it is not quite polished enough for wp repository release I think – but that is another kind of spam blocking issue.
Hope these tips help you, they have made a huge difference for me.
arg – tried to post a reply and I think it got akistmetted for having two links…
/wonders why they do not whitelist links to wordpress org / buddypress org here for that setting somehow.. sheesh