Its interesting when you look at MySQL database environments. Extremely popular in the MySQL world is to use commodity hardware and implement the LAMP stack. Smaller projects and startup companies love this environment. A simple example, a company needs to set up a web application, they buy some commodity hardware, set up replication and scale horizontally. Everybody loves this and it works great.
This environment requires floor space, cooling, electrical outlets, etc. As new MySQL database servers get built, the environment needs to consider how this database environment will scale. Organizations may take a step back and start looking at scaling with blade servers or large host systems to run large numbers of MySQL databases.
Database servers are I/O intensive. Growing with cheap disks does not always scale with systems that have large I/O requirements. Striping and mirroring starts to become more important. So storage scalability and more expensive storage solutions become a consideration as I/O increases.
It will be interesting as Sun leads MySQL into more enterprise environments how the hardware and scalability strategies will evolve.