Here is a quick summary for those of you who don't want to read the whole article:
Always use strict doctype and standards-compliant HTML/CSS
Always use a reset at the start of your css
Use opacity:0.99 on text elements to clean up rendering in Safari
Never resize images in the CSS or HTML
Check font rendering in every browser. Don't use Lucida
Size text as a % in the body, and as em's throughout
All layout divs that are floated should include display:inline and overflow:hidden
Containers should have overflow:auto and trigger hasLayout via a width or height
Don't use any fancy CSS3 selectors
Don't use transparent PNG's unless you have loaded the alpha
