Iconoclasm is a tweak that lets you break the barriers of what you can do with your icons. Previously, you had to deal with multiple extensions that didn't necessarily play nice with each other, or use blank web clips. Not anymore.
You can define as many rows or columns you want. You can even break free from rows and columns, and simply have icons placed freely on your home screen. It's all up to you.
After Iconoclasm is installed, it will appear in the Settings application. From there you can select a layout that will be shared by all pages, or turn on Per-Page Layouts and select a different layout for each page on your SpringBoard.
Layouts are property list files (plists) stored at /Library/Iconoclasm/Layouts. The format is pretty obvious if you're used to dealing with plists, so start by checking those out.