With old style theming in a package you could base your themes on Sunburst or classic. Creating themes based on frameworks got me to do the theming on the content side and then move the complete body over to the theme side. After several variations of one type of framework the constant duplication of resources, made me realize I needed some form of inheritance for this type of diazo theme.
The greatest thing to me about XDV is that you can leave Plone as it is and alter nearly everything about it. Mostly xdv will suffice, but when necessary you can even grab for xsl. You're not even doctype bound. I've been working on an XDV theme based on HTML5 boilerplate.
With Plone's new theming mechanism it is a breeze to conform to a strict doctype necessary for the Dutch Web-guidelines (Webrichtlijnen Overheid). This post is actually long overdue since I've done this at least half a year ago, but still, better late then never.