Dave seems to do as much work on his car as his house. He suggested for a real solid patch in drywall, use auto body putty, that epoxy mix that you use to fill a hole in a car body.
Dave, I can't go along with this one. This stuff is expensive, hard to apply because it is so plastic like and takes a power sander to smooth it down. In fact it is very difficult to sand a hard material sitting in a soft material without gouging the soft stuff. I agree that once done you have a fantastic patch, but with far too much work. There are really good plaster products, like the Lepage InstaFill that fills large holes without shrinking or cracking and is so light that it won't sag either. In addition it sands easily. Why bother with an epoxy mix?