Every site that I develop uses Panels, so obviously I think Panels is an essential module and should be included in Core. The average user can easily install Panels and within a few minutes be creating custom pages and layouts. Posts, views, and blocks can be inserted anywhere on your page. If you don't like the layout, click-click-click and you have a new one. I promise, the only thing easier and more flexible than Panels is Panels 2!