I believe you answered my question, but maybe I need a little more explanation...

So as the current flows into or out of the input pin of the 8051, there is always resistance and capacitance. That of course makes sense, but how does the size of the pull-up resistor come into play? Why does a 10k not cause this, but a 1M would? Now where does speed come into play here? The more capacitance, the longer a change from low to high or vise-versa?

Thanks,
Phil