David Carr at Baseline wrote a fun article, "MySpace: Too Much of a Good Thing?", that talks about MySpace's effort to scale to their rapid growth and the trouble they had with some of their attempted solutions.
As MySpace VP of Technology Jim Benedetto said, "We made a lot of mistakes." The biggest appear to be putting all data into a relational database (an SQL Server database at that) regardless of whether that was needed or appropriate, inadequate partitioning of data, neglecting opportunities to cache, and investing in scale-up rather than scale-out of hardware.
[Found via DeWitt Clinton]