Konstantin Käfer (aka kkafer) gives an overview of his Drupalcon Paris talk on optimizing the front-end Javascript and CSS -- including some YSlow tips.
Konstantin also talks a bit about his Support File Cache module that allows additional front-end optimizations by allowing you to control the bundling of CSS and Javascript files.
He also talks a bit about the Front-End Drupal that he co-wrote with Emma Jane Hogbin.
Finally, Konstantin talks a bit about some of his favorite changes in Drupal 7.