Mr Howard Mr Fine,
I'd like to see the context that those notable authors have encouraged the use of 'progressive degradation' as i'm nearly certain they would say the same thing as me in this case - Use methods that work in all browsers wherever possible, they certainly would not be encouraging people to dismiss the styling in IE6. By all means use advanced CSS to make more advanced browsers look better. In this particular case you should use a simple class name if possible so that IE6 users(the majority) can see your style.
I'm actually quite shocked at the disregard for this browser so quickly after IE7 has emerged. As if overnight it became an antique and we no-longer needed to care about it's users. That is a grand grand mistake.