First, great plugins.
1) If a user tries to register a restricted username, it'll tell them it's invalid. But I'd like to provide a custom error message, saying that the username is unavailable. By just saying it's invalid, it can make the user feel they've entered a username with improper formatting, and not because the username is restricted. They could end up abandoning the registration process.
2) It would be great if there was a log kept of failed registration attempts due to invalid usernames chosen. This will help craft a better fail messsage, as I'd mentioned above. Currently, I don't know how many people may be getting tripped up trying to register invalid usernames and/or if I may be restricting too many usernames. Having a log will help determine that. Also good for potential debugging.