The first thing to do while checking out an overloaded blog is to see if it's being spammed. It is one of the top reasons why blogs run high on CPU usage. Check the "Comments" section in your WordPress install. If you're seeing the same sort of comments as the mail you see in your mail account's Inbox from spammers, you'll need to install a plugin to help deal with the incoming flow of spam.
There are a lot of anti-spam plugins that are available for WordPress. For example:
- Pros: Spam checking happens off server, low impact on server overhead, works with most feedback forms.
- Cons: Needs an API Key in order to run.
- Using a combination of plugins is recommended, but keep in mind that the CAPTCHAs plugin is not always user friendly.