I went through and tried to account for all of the CSS selectors that'd be applicable to Wordpress 2.7 comments. http://cdharrison.com/2008/12/threaded-comments/ Sample CSS is available as well as an empty template for inclusion in Wordpress themes.
I then took it a step further by creating two sets of "Style Starters"... hopefully these will be of some assistance to Wordpress users/theme developers:
Style Starter #1: http://cdharrison.com/2008/12/wordpress-27-comments-style-starter-1/
Style Starter #2: http://cdharrison.com/2008/12/wordpress-27-comments-style-starter-2/