"making Drupal web sites load faster. 80 to 90% of the response time (as observed by the end user) is spent on downloading the components of a web page. Therefor this is also the part where optimizations have the largest effect."
http://stevesouders.com/episodes/
"wrote a simple Drupal module — the Episodes module — that could create simple charts to compare the average page loading time per day per geographic region."