The Mcnaughton is an excellent system. There's a few "tricks" to keep in mind.
1. Cutting tip should be dead on the center line. The enables the shape of the knife to stay within the "kerf" of the cut the best. By going higher or lower, either the top of bottom of the blade will rub more.
2. The most common cause for "dislodges" are "sudden bursts" or "jerks" into the wood. The smoother the feed rate of the knife the better the results. One way I control this is to hold the handle with one hand (right) and my left hand I place at the backside of the support, just under it, as the knife enters the support rest. By squeezing or loosening my grip of the knife at the support I can better control the feed rate to a smoother cut. I think this is also mentioned in Mahoney's DVD.
3. To start, I'd recommend a 12" blank and low speeds. I usually core at approx. 500 rpms. Green wood is the way to go. Dense or soft woods both core wonderfully. Use what you've got.
4. The knife as it cuts will always "bind" first on the outside. I usually cut 1/2 way through the blank and then pull out. I start another cut towards the center abot half of the cutter's width over. Just enough to "widen" the first cut to the outside of the knife. This also creates a wider kerf so the ribbons can exit the kerf. On large blanks, I do even slightly move the banjo in towards the center slightly. On smaller blanks I find just moving over the kerf slightly will widen the kerf enough to give the knife's outside edge room.
5. By "lapping" the edge with a hone, up the tool to raise a burr, you should always have a sharp tool.
6. You can go from the outside, bigger bowl in, or form the inside out, smallest bowl out. I find for learning, it's easier to take the larger bowl first, rechuck the "center core", turn a tenon and do it again. You'll end up with maybe one less bowl due to the tenons but I think you'll have better success as you learn the system. 2 or 3 bowls is better than just 1.
7. Also take a look at Bill Grumbine's second bowl DVD. He has some excellent tips as well.
8. If you have questions, feel free to ask anyone. Mahoney and Grumbine are excellent turners and very nice guys. I'd be glad to help to "troubleshoot" any issues as well.
Have fun.