I’ve been looking in Firebug at the Net tab where it shows the size of files.
A lot of high traffic sites seemingly have surprisingly small initial GET sizes for the url.
For example, GET www.hostmonster.com comes in at 3.9KB. (Apologies to those who are offended by the example.)
If I put the hostmonster HTML source into an editor, though, it saves at 12KB. If I run it through an online compressor, it only reduces it to 11KB.
What is going on that it’s down to 3.9KB?
Use Gzipping. Check out the most recent CSS Tricks screencast it will take you through many techniques to speed up your site and will describe how to setup Gzipping much better than I can here.