If comments are used extensively admin can create a report about all user comments in the system. They can delete the comments also.
This feature makes specially sense to find and delete spam entries by keywords or inapropriate terms. My suggestion is to add a keyword search to the report: comments page.
There is a spam search by keywords for user accounts. Often the terms for search in user accounts and comments will be the same. Its also an option to expand spam search in user profile descriptioin to user commenst entries and to report them at the spam page.