Many people are not aware that the square boxy drywall look does not have to be the norm. Simply replacing regular square drywall corners with round or bullnose corners can completely change the look of a room. You can even get ones made out of vinyl specifically made to curve through arches.
One of the problems with bullnose drywall corners is how to match them to the floor moldings. You can get vinyl transitions from the rounded to square and use a regular square corner for your floor molding. You can also put special rounded wood corner moldings at the bottom to match the drywall corners and simply butt the lengths of wood floor molding into them.
Goldline makes metal corner beads that are covered in paper and applied with glue or joint compound and no nails. Trim-Tex has a full line of vinyl in either ridged and flexible beads. The Colonial Corner Clips shown on this show have gone out of business, sorry about that.