This blog forms part of the http://performanceGuru.com website which focuses on performance tuning UNIX-like Operating Systems (including Linux).
Sun have put together a very good webcast
which highlights how they are transitioning their expertise in large NUMA type systems into the challenges of smaller horizontally scaled technologies.
Obviously one of the main thrusts of this webcast is threading, although it was refreshing to hear the chat to be fairly platform agnostic with discussion of both horizontal and vertical approaches being discussed.
One of the things that came across to me in this presentation is that really they are facing the same challenges in the vertical and horizontal environments, its just when you solve them for the horizontal you have to operate in a smaller solution domain and be more creative, as you cannot offload these complex issues to the system hardware.