I've added a few more checks to this plugin. Most of these replicate what you can do with saved searches, but I just found it convenient to include and saves the user the effort of creating them.
Additions to v1.1:- Find books with comments that have no HTML. Note that this is not the same as inverting the "comments with HTML" search results. This search finds books with no HTML at all be it style tags or paragraph/div tags added by Calibre when you save from the Edit Metadata dialog.
- Find authors with commas in name (for people who use FN LN)
- Find authors with no commas in name (for people who use LN, FN)
- Find titles with possible series info (searches for hyphens or numeric values in the title).
All three of the latter searches can be customised within the search dialog so you may choose to make them more specific to how you require your authors/titles to be stored.