the problem with mating plaster with drywall is that it's very very hard to match the surface's drywall is so smooth and plaster always has a bit of texture too itthere are some surface treatments that you can trowel over the entire wall to give it a singular surface it's called... sand surface, or trowel on or some such thing you can actually mix paint in with it and then you don't have to paint it when your done...
Ya, that had actually concerned me. The two walls I did drywall are at a corner (both ends), so it wasn't a big deal. But now that I've gotten down to the plaster, I noticed it's not smooth. I was doing some testing last night and watered down the joint compound and smoothed over a section to see if I could do something about that. It seems better today, although now I have to sand it :( Another thing I've found is that there are a few spots that someone did some patchwork, and not very well. It's really hard stuff, and I'm attempting to scrap down the edges, and then fan it out with the joint compound. I hope that works. I don't mind normal inconsistencies in the plaster, as I think it adds charm to the house. I always wanted an older home and I'm thrilled that I'm so far able to keep it original. Although some dumb ass took the slate roof off. Someday I'll put one back on it, as well as on the carriage house. It's really neat. Our carriage house was built to look just like the main home, except scaled down.