@Paul -

Fair enough.

But, if the "Thesis" name isn't trademarked (for the sake of argument, as I'm sure it must be trademarked), what remains as a cause for a legal suit?

(Of course, if that "Thesis-like theme" also happened to incorporate the copyright-able content of Thesis, such as its cutsom functions, etc., then that is another matter altogether.)

I would hazard a guess that the "Thesis-like theme" author could plagiarize the Thesis style sheet 100%, and still survive a legal challenge. I'm not aware of any legal precedent regarding plagiarism of a CSS file (or an HTML file for that matter) - although web plagiarism has been prevalent since the days of HTML 1.0.

The bigger problem, though, for the potential plaintiff in such a case, is that the same output can be rendered exactly, using an entirely different style sheet.