I think this is needed for more than the service catalog.
I take it you're looking for more than the LANDesk guides that are available for each release? I'd imagine support hasn't done anything more (though I find the guides really useful - just before Karen lynches me!!) as each system can be different so doing a complete step-by-step guide wouldn't work for everyone. I know I've created user guides for fellow Admins but these are tailored to how we use the catalogue and how we've customized the product. Have you checked out the eLearning section? I haven't watched this but it's probably as good a starting point as anything - though as this was v7.4 and the Add to Cart wasn't available it won't be documented in it. http://community.landesk.com/support/docs/DOC-22322