There's no shortcut to switch to the standard Today screen-- the only way is to go to Today settings and change the today screen. That said, you can use any and all standard WinMo Today screen plugins with the Samsung 1 and Samsung 2 Today screens. But if you love the Widgets home screen, then there's no easy way to get to the traditional view.
So far no touch screen phone is like the iPhone's (lucky Apple). The Omnia's sensitivity seems well-suited to the TouchWiz UI. It's hard to compare it to the Diamond directly since the Omnia has haptics and haptic screens feel and behave differently from traditional resistive touch screens. But I'd say that the Omnia's screen is definitely more sensitive than the Touch Diamond's (requires less pressure).
A stylus is included, BTW-- but there's no silo to store it. You've got to attach it via the short cord to the lanyard mount (I'll include photos of it in our full review that's coming out later today). The only times I've needed it though were 1) to demo gaming for the video so I wouldn't block the video camera's view 2) handwriting recognition (which I don't bother using much on the Omnia).