Custom Query String is no longer supported, however, I've heard. It still works on my blog, in WP 2.2. I'm using it. But I don't see how I could use it to achieve what this thread asked exactly.
You could use CQS to set your Day archives to display all the posts from that day (-1 is all posts).
WordPress already makes a Day archive (and a Month, and a Year). Just type the right permalink and it comes up,
example mysite.com/wordpress/category-date/2007/05/31 -
normally displaying the same # of posts you have set in Options > Reading. You can adjust that # with CQS.
But I don't think CQS will help you make a Day archive with -1 posts showing, into your Homepage or index, which is what that old WP option was supposed to do (IIRC).