With my favorite code editors, the convention is: If I select multiple lines and hit tab, it indents it all. If I select multiple lines and hit space, it replaces it all with a single space. 'Nuff said. IMHO this point alone makes tabs the natural choice to mass format lines of code. Sure some editors allow you to get around this by having options to convert the tabs into spaces (so you can still tab multiple lines, the editor just immediately converts them to whitespace). But not all editors have this, which means you may end up changing the format of your code depending on which editor you have open (e.g. VS2010 with the tab-to-space conversion enabled versus SQL studio which doesn't have the option AFAIK).