Over the years I've tried to re-paint these ceilings, and have never had good success with either a brush or a roller. Right now, I'm re-doing one bedroom in our house, and following some advice I got at Home Depot, I chose to scrape off the crap and paint. Using a 6" wide mud blade, it took me a total of maybe 4 hours to get the ceiling down to the original sheetrock and spackle. I used a respirator and goggles and yup, there was plenty of crap on the floor and on me. But I got it done, and managed not to gouge the ceiling.
I happened to be doing a home inspection where the owner was a lathman and remarked to his wife that they had done a great job of painting their popcorn ceilings. Turns out they used an airless spray gun, and no peeling or flaking at all. Use a roller and this crap will usually flake off in chunks as small as 1/2" to as large as 6" in diameter!
The wife didn't know much about the spray painter other than it was an airless unit. Might've even been a Wagner Power Painter for all I know. Can't imagine them using a industrial unit but anything is possible since this guy is a sheetrocker that specializes in sheetrock and taping... but not painting.
The biggest problem I've encountered when trying to roll or brush these popcorn ceilings is trying to match up the voids where the texture has flaked off in giant chunks. Plus they get wrapped up in the roller in small pieces as they fragment, creating even more of a mess as you try to paint. Just wondering about other folks experience (good/bad) with this stuff and how you did it. I'm tempted to buy a WPP and see if they are good for anything as I'm probably going to clean and re-seal my cedar fence this spring.