About the multi Megaherz Problem: I don't agree that this causes problems as long as the oscillation just occures between two states (which is normally the case), I just have to handle all possible states in software, as of course can also be done in HW using an Agilent $$$$ chip: Here is an expample that I used with position measuring in a robot system.
We have four states A B C D.
1) I detect the states all 50 usecs
2) if changed, then I compare to the old state and decide if it counts up or down and store the new state.
Now if a multimegaherz oscillation occures between A-B i would miss a lot of action, but the worst thing that would happen, is that my reading would accidentally change 1 digit quite unpredictable.
The part of the SW would do something like
every 50usec:

A=0;B=2;C=3;D=1;

new=P1 & 3;
if(new != old) {
if(old==A && new==B) x++;
else if(old==B && new==A) x--;
etc..

old=new;
}

However if I would miss B between A and C then it does not work anymore. So a complete state can't be shorter than 50usec.

Werner