I've set the option 'Preview posts' to 'required' (http://www.orocos.org/admin/settings/node). This helps reducing spam, since the spam filter already scans for spam during a preview, and can intercept it before a 'post'. Unfortunately, if you're frequently editing on the website, this previewing is quite disruptive for the workflow. It's maybe too much of a hassle for the low amount of spam we're receiving ?
Also, I've set the default input filter (for the whole site) to 'forum' which is a wiki text filter + glossary highlighting + email obfuscation. I found this filter the most intuitive to use (Filtered HTML is really a pain for editting). I could not find yet how to set a default input filter per content type (story, forum, page,...).