Nigel,
If you don't mind, I have some ideas about your tutorial that
1) May you give more clear and simple routines for beginners only? For example, you write it as timer tutorial, adc tutorial, pwm tutorial.... and it should be very simple to understand. Because, at the first time as I learn to write PIC, I cannot read your tutorial.
2) Do you work on motion control? Have you done a tutorial for PID control with PIC 16f876? And some other project such as fuzzy control... Yup, we can found those application notes on microchip site, but i think they are not popular, because people usually use mid range pic more than high end. And they did it with C codes. A mpasm tutorial on these project should be helpful for beginners.
3) If you don't mind, you can tell techniciens on this forum to give you their hands. And I think you tutorial is very very good. If it has more project, it will soon becomes perfect.