I was delighted to discover that Android 2.2 supports the position:fixed CSS selector. I\'ve built a simple proof-of concept, here:
http://kentbrewster.com/android-s
This will probably not be resolved until Android switches to using Chrome for its WebView. The current Android browser creates an Android TextView on top of the page when an HTML input field is focussed. Apparently they don't style or position it correctly. You can see it go more wrong on pages that use contentEditable.
The current Chrome-for-Android implements the WebKit IME interface, so input fields are drawn by WebKit (and lose some of the niceties of the Android TextView on ICS) and shouldn't have issues like this.