I got a specific request from a blogger asking whether 3-column templates are possible with Blogger Beta. If you have a lot of items in your sidebar, you would naturally want 3 columns like him so that you can balance your items across 2 sidebars. I found that it is in fact easier to convert Beta templates to 3 columns than older templates. This is because the condensed form of template shown by Beta is easier to work with. In addition, once you add another sidebar, you can move page elements between the two sidebars easily using the Layout editor.