A good (and very technical) book about the advantages of cluster archtectures. Also provides a very detailed analysis of programming modesl (608 pages) ISBN 0138997098 This book is seems to be out of print.
In Search of Clusters by Gregory Pfister
http://www.amazon.com/exec/obidos/tg/detail/-/0138997098/ref=pd_cps_eb_1/104-1154502-8274348?v=glance&s=books