@y00tz: Err, not that you do it wrong per se, but that you're trying to deal with the cross-browserness the wrong way. The recommended way that has a far higher success rate is with CSS hacks. Browsers like to lie about themselves for compatibility sakes.
Although I do do it the more accurate way, I do only target a very limited market: IE6, IE7, the latest version of Opera, Firefox (Gecko and related), Safari, and maybe mobile IE and mobile Opera. Although, usually targeting for IE6 gets most of IE5.5.
(In other news, IE8 passed Acid2!)