Users that consistently use more than 5 tabs *need* to have the option to put tabs on a separate row from the address bar. I've read the blog about the vertical space and UI aesthetic reasoning, but having the tabs locked onto the same horizontal bar as the address bar will make IE9 a nonstarter for a lot of tech-savvy people - your most heavy users. The common masses (e.g. our families, etc.) look to us for advice on which products to use. It'd be a shame if we have to start referring them to another browser because of this one feature change from IE8.