The 80/20 Rule

"40-60% of Yahoo!’s users have an empty cache experience and ~20% of all page views are done with an empty cache." - says a yahoo research.
This is a shocking conclusion: if ~20% views are done with empty cache then definitely we should pay more attention on not having to0 many HTTP round-trips in a page. Easy to say and... to do (if you think a bit more).
Ok, now let's assume you have structured your front-end in a maintenable way and more: using static includes, you've managed to have just a few HTTP request(1 html, 1 main.css - huge one (as it statically include other css files), 1 javascript - a bug one and 5 images) , but what do you do with the user experience? [trick situation, isn't it?]
If you have a nice roll-over horizontal menu (nicely created with lists and css), an end-user with a slow connection, will see first the menu ordered in a normal list and after a few milisec the list turns into a nice menu => not a nice user-experience!!! My 2 cents: load you menu.css first and then the main.css...