"was amazed to see that there is almost no debounce. my ISR code never gets executed more than once most of the time (maybe 1 in 100 tries it gets executed twice)."

1 in 100 failure is just out of the question for any serious industrial application!! Can get by with in college projects and some toys maybe.

I would endorse a full software debounce when possible - gives so much of precise control over the timings for fine tuning. And when multiple inputs are there will work out quite economical.

One possible place where software debounce cannot be used is when you are using the T0 or T1 to count an external event like limit switch closure ?

Raghu