a few pointers
Yanmar advises not to run the engine when the boat is heeled over 17 degrees. In my way of thinking, if you've got enough breeze to heel that much, you shouldn't be motoring anyway.
Off the coast, I often see people motorsailing with the main overtrimmed. I suspect this is because they're not really using the sail for propulsion, just as a stabilizer. This seems goofy to me, because if the sail is drawing properly, it will stabilize the boat better. Of course, a strapped main won't heel the boat as much as a main in proper trim, so perhaps this is what folks are going for. Motorsailing becomes a way of battling seasickness, especially in situations where the breeze is light but the swell is not.
If you're motorsailing correctly, you still need to tack into the wind. You'll be able to point higher than usual because the apparent wind (generated by the engine) moves forward.
As far as the rules of the road are involved, when you're motorsailing you're a motorboat, not a sailboat. Which is why the rules specify that you fly an inverted black cone--apex down--in the rigging during the day, so that people don't confuse you with a sailboat. Out here on the West Coast, if you see someone flying the proper signal, it probably indicates that they are cruisers from Europe. The rest of us generally ignore this rule during the day, but at least know enough to run the steaming light at night.