I know one thing that makes cranky all web developers who still support IE 6. Usually we can hope that soon IE 6 became history ( maybe Windows 7 will be so good... and everybody use it and new IE ). But yet many designers still support IE 6. Main trouble that IE does not cache CSS background images. And that's why you see "flicker" effect on reload of you well formed css sites. To get rid of this try to add this script somewhere in the HEAD section... 

[code=js]

try

{document.execCommand('BackgroundImageCache', false, true);}

catch(e)

{}[/code]

 This works for me.

ps: You can see this effect good in AJAX.NET Tabs control. http://www.asp.net/AJAX/AjaxControlToolkit/Samples/Tabs/Tabs.aspx