I read a post today on Nicholas’ blog which indicated that he was having trouble commenting on my site. I’ve had other commenting problems (1, 2) in the past which have been traced to my spam-blocker, WP-Gatekeeper. I haven’t spent any effort on the current problem, I’m just assuming that gatekeeper is at fault, so I disabled this plugin and installed Spam Karma 2 since Nicholas seems to be getting good results with it. I’m not sure what Joseph is using nowadays, but gatekeeper may be doing the trick for him–I found out a few days ago that he hand-rolled his crisp minimalist theme, and perhaps gatekeeper plays well with such a setup.
I’ll run with Spam Karma 2 for a while and see how it goes. I hate to think that people might have tried to post comments here, failed, and given up on this blog. I really have no idea how many people read the crap I post, but I know there are at least a few people out there with too much time on their hands. 
Sometimes way, way too much time.
I’ve been really pleased with Spam Karma so far; for most legitimate comments it’s completely invisible to the user, while most obvious spam is blocked silently. For stuff that falls somewhere in between, the user has to solve a captcha to prove his or her status as a live human being. What I like best is that it incorporates all the major approaches to spam blocking in one plugin — blacklists, keywords, captchas, IP logging, JavaScript, comment moderation, user levels, link counting, hidden form fields, HTML entity detection, post age, etc. On my system (which receives relatively little spam anyway, not being particularly widely linked), it’s blocked 96 spam attempts since I upgraded from SK1 to SK2, while approving 24 and only requiring me to manually moderate 1.