Anandtech did a great article covering the Radeon 4870/4850 success story and how it was a major change in the way GPU makers develop their chips; instead of designing a monolithic GPU and scaling it down for lower performing parts, they developed a much smaller die and implemented GDDR5 memory (first of type) on the cards, rather than trying to take the performance crown. This resulted in an unprecedented price point and is what turned AMD/ATi's fortunes around.
Thanks, I remember reading that. There ws another equally in-depth article later by someone else which followed on with the development of the 5000 series, and how it continued from the lessons learned there.