Searching through google about stud nailing crown molding, I found this page about whether or not it is necessary to hit the studs. Can anyone confirm that it can be done without worrying about the studs? I'd prefer not to mark up my wall with stud locations and it seems like quite a bit of extra work.
Crown moldings, or any corner trims really should be nailed to a stud, not simply into unbacked drywall. Without good support, the molding will warp out from the wall causing gaps in coverage to open along the edges.
With real crown, there is a hollow gap behind the molding as only the top and bottom edge touch the wall. The wider the molding, typically the deeper the void behind them. This gap results in having to use longer nails to reach the wall and support wood behind the sheetrock.
One method that works well to make installing the molding easier is to first install a backer/nailer to the wall. Depending on the size of the hollow behind your crown, cut or rip some scrap board, plywood or even strapping, then nail it along the top edge of the wall against the ceiling. You can shoot as many nails as you want to assure the backer if firmly attached to the studs or wall plates, as it will never show anyway. Now, when you go to nail your crown up, there will always be a solid wood backer anywhere you shoot a nail. You can also use shorter nails, or at least not have to use extra long ones. This method is also helpful when your walls are not perfectly flat and an extra nail is necessary to draw the molding in tighter to the wall in irregular areas. Good Luck
For crown molding, I would. In addition to the home shifting over time (heat/moisture expansion and general settling) you're also working against gravity. Chances are slim that it would fall, but it could start to pull away and leave cracks.
In most homes, the studs are easy to hit. They're equally spaced from one side or another, 16" apart (though the end will be slightly off for the corner). Instead of marking the walls up, mark one stud on the wall, test fit the molding, and then mark the molding. You have to touch up the molding with filler and paint at each of the nails anyway, so the marks there should be no big deal.
If you're set against trying to hit the studs, then at least put two nails in at each location pointed to each side. This way the nails can't pull straight out. The down side of this is if you ever have to take the molding down, it will make a mess of the walls as the nails pull through the drywall. If you hit the stud, chances are the nail would pull through the back of the molding as you pried it off the wall.