Nielsen's group conducts usability seminars from time to time. What follows are my somewhat arbitrary condensations of three sections of Nielsen's book. He probably wouldn't recognize the content so don't blame him. It could be enlightening. The most popular sites load twice as fast.
Web users rank slow download as their greatest annoyance.
Keep your page download sizes to 32KB or less. That includes unique graphics. They won't know what to expect and they want to be in control. If you use graphics, make them small but decipherable. Try to re-use the same graphics from page to page.