I recently did some searching on debounce and software debounce. There's a lot of variance in views out there, depending on the goals and determination of the people with them.
Here's someone not satisfied with just making a reasonable product and reporting success:
If you get the right switches/buttons instead of a randomly chosen array and you can come up with reasonable debouncing but the time period I've seen shown for mechanical contact switches is more than 1/100th of a second. Sometimes it's more like 150 ms.
The thing is that 100 msec is reasonable in most all cases. I never before had reason to time any closer than gross human perception. As long as I didn't get false returns and it wasn't too slow.
Yes you -can get- buttons and switches capable of much faster debounce and they're not special order items. My keyboard is probably way better than 100 ms but at my age, I'm not fast enough to hard-test it.
AFAICT the best debouncing is done in hardware.
My best cap sense results were 'fuzzy' logic but I was getting definite ranges for touch, finger close, finger away in under 5000 usecs without actually calculating RC time. That was using a 1 uF cap and 330 ohm resistor in parallel between a digital pin and ground. I actually got good repeatable responses under 3000 usecs maximum with that RC combo but I know since I could do better because I finally read up on RC time constants instead of going by intuition and trial. Fun part to me is when my home-made paper and foil elements fuzz over the speed of a really fast setup.
But with more than a couple-three hours I am sure I could do better, and I am no pro. I bet Nick or Mike or any of dozens of others here could do better in under 5 minutes including time to warm the iron and hunt for materials.
And then I ran Mario Becker's demo, holy crud it's fast! That was 3 days ago and I'm still thinking. Only problem I have is in bare wire contact straight into my pins. One time static and that's probably it for my UNO.
It's still amazing to me: http://arduino.cc/playground/Code/CapacitiveSensor
I look inside my keyboard and what's under the buttons? A cap sense membrane and a logic chip.
Now compare that to what an engineer found using a varied array of buttons and how big is the ballpark?