First of all I second Lee.

The technique you put forward is not new, in fact it is exteremely old. The results are never as good as with a dedicated ADC.
BUT if you don't need much, for instance you only need to read one or two potentiometers on a control panel with low resolution, it's an interesting alternative.
Keep in mind that PWM with a LPF will also give you DAC capability, so if you want real simple, a resistor, a capacitor and a comparator will give you a crude ADC already. Which will sometimes be a good, and sometimes be a bad idea. It depends on your requirement.

Point 2 about the interrupt makes no sense to me. After you output your DAC value, you can (almost) immediately take a look at the comparator output. What would you need an interrupt for?