This is a concise, useful overview of the questions one needs to ask and answer when creating cultural variants on established 4e "races," which have always seemed like species to me. It offers a framework for addressing these questions, based upon identifying the key cultural traits of the default version of a race and then creating variants by exaggerating, opposing, or twisting those traits in some fashion. The examples are brief but well-chosen to illustrate the points being made.
The .pdf is quite a nice length for an onscreen publication, actually, because it's easy to read through. That being said, it is well-bookmarked, something many book-length onscreen documents don't bother with. This supplement won't help someone seeking detailed advice on how to create a culture or a new species; rather it provides helpful mechanical guidance for how to reflect your own ideas in the most efficient fashion using D&D 4e stats. Recommended.