The option to allow anyone to register to your WordPress blog is basically useless and should be removed. The reason why I am saying this is that once the automated spam bots find your blog, they start registering users in the hopes of using your blog as a spam distribution platform.
You can use CAPTCHAs as a gate keeper to your registration dialogs. But the fact alone that this is necessary angers me. Just because a bunch of rightfully underpaid software engineering dropouts thinks it is a good idea to support the spam industry, the rest of us have a harder and harder time using the Internet for something useful.
I hope that later generations will look back at this advertise-any-crap-anywhere madness with mild amusement telling themselves that we were a bunch of brainwashed consumers who just didn’t know better.
You there, spam bot programmer you proved that you at least know the basics of software development, make something useful out of that and improve your karma.