Version 1.1 of Client Power Tools adds client deletion. Now you can delete a client from the client’s profile, under Edit Client.
Be careful. Deletion is permanent. There is no undo. When you delete a client, it will delete that client’s WordPress user account as well as any messages associated with the client.
This is as good a time as any to make sure you have a solid backup solution in place for your website, including the database. Your hosting provider is probably already backing up your website and database for you, but you should make sure you know the backup schedule.
For an easier option to manage yourself, VaultPress, from the builders of WordPress, is an easy-to-use, affordable backup service. But there are many others.
As always, I would love your feedback on Client Power Tools. Let me know what you think on Twitter, where I’m @samglover, or leave a review on WordPress.org. If you have a problem and you can’t find an answer in the documentation, try the support forum.