Thanks everyone for your help. I was hoping to find out the actual math behind choosing a 104 cap and the 10k and 470 values of R1 & R2. However, the explanations are indeed helpful.
I have tested the other circuit that uses only a resistor and a cap (I'm using 10k-ohm and again a 104 capacitor) and this is working just fine. Again, what is the math behind these being the "magic values" when dealing with +5v input?
The other way to debounce is to get rid of all that stuff and just do it in software.
Yeah I'm fully aware of software debouncing and how to implement it, but I am using an ATTiny chip for the uC on this project so code size is an issue. I am already using half of the available code space and I have only implemented two of three interrupts required and none of the sound output.
Plus this is a great opportunity for me to learn a little more electronics theory. I am a very competent software person but somewhat new to figuring out all of the electronics on my own.
I might just turn this project into an Instructable too. I think a few people might enjoy spending part of a weekend building this contraption.
Now I need to figure out how to (or even if I can) use a voltage divider circuit on a rotary select switch with a pin-change or hardware interrupt. I might just have to "simulate" the interrupt by checking for changes to the switch-pin voltage in loop() but I prefer the more elegant "interrupt" solution.