This is a great module and almost exactly what I need for my site. However, I'm finding that I need more flexibility in my layouts than the module currently provides. Rather than ask bengtan to create layouts for every use case (as I'm sure he has better things to do), here's a patch that allows site administrators to add their own custom layouts without modifying composite.module.
The method is borrowed from Panels. Basically, I've replaced the hard-coded array that defined the zones for the layouts with a pair of functions that scans the theme directory for inc files. Then I added an inc file for each layout that itself contains a function that builds the array item for that layout.
To add a new custom layout, all the site administrator needs to do is place their custom tpl.php, css, png, and inc files in the theme directory -- the functions will find the files and add the new layout option.
I've tested it on my site, and it seems to be working well. Let me know what you think.