Nice article about how MySpace has scaled its website during its continuing hyper-growth. My summary in 256 characters (the del.icio.us limit for 'notes'):

2*web,1*db>N*web>master-slave dbs>db-per-feature>SAN>partition tables (but 1 login srvr)>ditch coldfusion for c#/asp.net>upgrade SAN>add distrib. caching, finally>go to 64bit DB/OS>fight MS limits>face cascading power outage>now: adding geo redund. to SAN