Simply said, "Just because you can, doesn't mean you should" . I have noticed that I am saying this phrase to myself more often than not with SharePoint. When it comes to SharePoint Branding you/client/developers have allot of choices to make. Its never as easy as you think. I find myself going down the rat hole of making it overly complicated not because I don't know what I am doing, but because I know I have the power to do so. Within SharePoint master pages you have the ability to change the default class names. For example if I wanted to change the class name within a custom master page for the quick launch (ms-quicklaunch) to your own custom class (xyz-quicklaunch) its very easy to do in the master page. However you might be getting yourself into allot of headaches because with out really thinking about it you might have totally screwed yourself... Since you now have stripped that main class out of the page all of the default references to ms-quicklaunc...
By Erik Swenson - Senior User Experience Designer