Can you be more specific about the problem you are seeing with the input keyboard in landscape mode?
As for the ScrollViewer, I believe there are two issues here:
In the Beta release the ScrollViewer only shows the scroll
bars while scrolling. They fade in when the user starts manipulating the content and fade out again when the user lifts their finger.
The WebBrowser control
internally handles scrolling of the web content and so the ScrollViewer never get's the manipulation events.