Unwanted Comments: Comment spam is becoming a bigger and bigger problem. Shirley has a good roundup of resources to help you fight it.
“Some site owners stave off comment spam by closing off older comments, using blacklists, using filters, just deleting them when they occur, or a combination of these. Below are some good possibilities along with my comments and thoughts about what I’ve implemented so far.”
This may be a good argument for using a discussion board as a blogging system – or anything that requires some kind of log-in or membership capability.