In summary, the IE team is urging developers to clean up their CSS hacks to prevent issues with IE7 builds. The use of hacks in older versions of IE has created complications, as IE7 will make life harder for those who relied on them. The release of IE7 (the browser) will enhance the functionality of IE7 (the script), potentially aligning IE6 and IE7 behaviors. Although there are drawbacks to this approach, it may be less painful with IE7 (the script) available. The use of conditional comments and Dean Edwards’ contributions may also influence how developers navigate these changes. Overall, it’s best to wait for IE7 beta with new CSS behaviors before making any drastic changes.
https://meyerweb.com/eric/thoughts/2005/10/17/ie7-and-ie7/