Yslow is a pretty good tool to give you the basic information on web performance.  Keep your images small.  Make less calls to the server off of the page source.  And put the javascript as low as you can in the page load.

The problem is that if you follow this advice you can hurt your revenue and user experience.

Many current revenue models are counting on advertising dollars to carry the costs of operations and development.  This must be kept in mind when taking the advice of Yslow.  When Yslow tells you to put that javascript at the end, ask yourself what are you sacrificing? 

Pray that it isn’t revenue, or your click through reputation.  The prefered method of delivering ads is currently javascript.  In the end, the person paying for advertising wants to know about click through.  One thousand impressions and zero click through will get you no repeat advertising sales.  There are things that are good and not so good to move.  But remember, moving javascript is just a trick to the load order.  The total time to load the page will remain the same.  So the user will not get control of the page until all javascript has completed processing…. Regardless of how well you shifted the javascript.

Instead of following Yslows advice completely.  Consider Whyslow to give you reports as it happens.

Yslow takes a page load and tells you how to improve. 

Whyslow has ongoing sampling of your web performance.  Combine our performance data with yours, and we can correlate you backend cronjobs that might be creeping in during heavy traffic periods.  WhySlow can show you where it is and where it was slow, and help you track down and event that has passed.

Our advice for sites that depend on advertising revenue is to get the ads up there first.  It is like when you are eating cereal and you have nothing else to read… you read the cereal box.  Those ads are ok to show up sooner than later.  And besides, more and more ads are entertaining.  If your revenue model is based on advertising, then embrace that.  Recognize that click through, honest click through, is important to your advertising customers.  If you can get the ad to be relevant, and you can improve display time to allow it exclusive consideration on your page, for even 1 second, Whyslow guarantees that your click through rates will be improved.  Give the ad time to engage the users.

When your revenue model depends on advertising revenue, advice from Yslow needs to be tempered.  You have to make your site fast around the advertising.  If you find that certain ads are too slow, call your provider and see if they can help improve their performance.  Maybe you can cache the content on your side. 

In this world of Advertising Based Revenue, you need to get on your game for the money.   Whyslow can even help you keep track of the performance of your third party providers.