IE7 and the demise of CSS hacks is about the IE CSS hacks that have been loved over time and are urgently needed for IE6 to make CSS layouts at least presentable on the IEs. With IE7, a lot will change - and some of them will no longer work.
Urgent recommendation: Switch to conditional comments and move the CSS corrections to a separate stylesheet that can then be loaded for the IE. Unfortunately, with this you can only add CSS elements for the IE, not hide non-existent elements from the IE - possibly you can do something with overwriting elements.
In the IE Blog is a list of hacks that will be problematic with IE 7.