There have been two major pieces on segmenting your traffic written over the last week at the blogs and news sites I read. Both very insightful and detailled.
It is an important element in the marketing mix, though at times a tricky one to apply to search.
Rand Fishkin at SEOMoz does a good job segmenting the intent of search from various sources and the visual ads are a nice touch.
Jennifer LeClaire, in an article over at NewsFactor, outlines segmenting visitors which when read after Rand's article shows further reach and analytics to use.