In the most recent ExpressionEngine build release, 1.6.6, the ExpressionEngine coding team addressed a problem we recently have been struggling with on a high traffic project we coded and manage.
Specifically, on high traffic websites, EE's statistics tracking can overwhelm the MySQL database because it locks a table each time it writes new data to the database. Because EE frequently writes statistics data back to the database, things can quickly get out of control.
For our project, we turned all statistics tracking off because we were not using this data. Additionally, we installed Solspace's new Tracker module/extension to track statistics on which articles were being read on the website.
Time will tell if this solution helps reduce the MySQL server load that we experience when the site has traffic spikes. Our fingers are crossed.