I'm using the 18F2431 too.
And I begun with the PICDEm MC LV board...

It's a great uC ! (UART, I2C, fast AD, 3-times PWM...)
I use it as a PI(D)-Controller for a BLDC-Motor.
And I use it for his fast AD-Converters in a CR-Tuning-Box.

The Quadrature-Encoder isn't very strange ... the whole business with this chip is to use the right timers for the right tasks and use the right prescalers !!

;-)