My buttons seem stretched, especially in landscape orientation. I can't find a property to adjust either on the UITabBar, UITabBarViewController, or on the UITabBarItem's themselves. (Of course, one answer would be to get an iPad...but that doesn't solve the need for a phone.)
For example, consider this simple Tab Bar Example - if I only could set the tab bar to auto-shrink as more buttons are added, or manually adjust the width to fit them all on the tab bar, I would be happy.
It is not possible to use the UITabbar with more than five visible buttons. You've got to write your own component.
Here at significantpixels.com / The iPhone Tab Bar Lessons From Reality is an article about the tab bar which explains in detail how to design your tab bar from a UX point of view. And the magic number of tabs is five ;)