Nick Carr has a nice piece which predicts a decidedly unrosy future for the server industry. As he notes in the last paragraph: Ultimately, we may come to find that the server was simply a transitional technology, a stop-gap machine required as the network, or utility, model of computing matured.
The reasons, he notes, are consolidation and virtualization. As far as the latter goes, clustering (e.g. Google) would seem to be an especially attractive option for many companies.