DRUPALCON 2012, an approach to performance problems in Drupal
Here's a few solutions when dealing with performance issues.
eCSSential is a JavaScript that loads on the requested page the lines of CSS necessary to that page to minimize loading times and bandwidth. It is especially useful with mobile development.
Another way to save bandwidth is to load on pages images which are scaled to the device requesting the page. Modernizr is a Drupal module that deals with this.
For testing the page performances on servers in different locations and using different software, webpagetest.org and akamai blaze are two useful resources.