Today I spent all day at work labouriously going over the so called xhtml that Macromedia Dreamweaver produces. Every page produced by my colleague had to be checked and cleaned, then tested in Opera and Mozilla. Mostly I was removing unnecessary and invalid mark-up, and fixing errors that IE ignores, but sane browser react too.
I didn't touch his many-nested-table designs, but in sections of the site that come out of Perl/XSLT, I re-wrote his mark-up from the ground up in clean modern xhtml, with clean cascading style-sheets, rather than the multitude of tables and "one style rule per object on the page" approach of Dreamweaver.
Dreamweaver, FrontPage et al. have two obvious problems:
These GUI tools may be good for rapid prototyping by visual designers, but they are lousy if you want your pages to be tight and correct.