Stop using CSS hacks now
Still using CSS hacks for Internet Explorer? Kick the habit now or you'll be sorry. Call to action: The demise of CSS hacks and broken pages at the IEBlog confirms what should not come as a surprise: IE7 will fix many of the parsing bugs that CSS hacks rely on. Using conditional comments is the safest way of dealing with CSS bugs in Internet Explorer.
Some of the CSS hacks that will not work in Internet Explorer 7 are these:
Update: Bruce Lawson has more on why you should Future-proof your CSS with Conditional Comments.