If you're interested in upgrading to the upcoming Windows Mobile 6 or purchasing a device with it, you might like to take a look at the interface. At first glance, it appears to be nearly completely identical to Windows Mobile 5. The Today screen, Calendar and menus have the same layout, though they have been polished quite a bit and have a nicer color scheme. The menus won't take up any more space than they already do, though some configuration screens still have the very bland "Windows 3.11" look to them.
It's nothing particularly spectacular, but interesting nevertheless.