One thing to keep in mind is the outbreak of blog spamming which takes advantage of the ability to make comments as an unregistered user. Moveable Type recently released an update with the following features:
"We've included a throttling measure so that comments from the same IP address can only be posted every N seconds, where N is configurable. We've also added a measure to automatically ban an IP address based on an abnormal number of comments from the same address in a short period of time."
