ADC Sample Code has a bug (it seems)

There seems to be a mistake, because the code did not work, and after my change, it did work.

MainLoop
    bsf        ADCON0,2        ;start conversion and wait for it to complete
    btfsc    ADCON0,2
    goto    $-2

goto $-2 is wrong, because it goes back 2 lines and starts the conversion all over again. You'll want to goto $-1 instead, to just test until the conversion is done.

However, I would reccommend this instead:

MainLoop
    bsf        ADCON0,2        ;start conversion and wait for it to complete

    wait_for_completion
    btfsc    ADCON0,2
    goto    wait_for_completion

Just to be safe. With the relative goto it could be a little confusing exactly where it jumps. With a label, there is no doubt. Of course, labels are annoying because you need unique names.