I would think that most projectors sold within the last 3-4 years would have been designed to project on a flat surface, but that is just an assumption.
Because home screens are quite small compared to what commercial movie screens used to be (does anyone remember the huge theaters of yesteryear? Those screens were humongous!) I think the main reason to use a curved screen is to decrease hot spotting with high gain screens for very low Lumen PJ's. Image focal or distortion problems should be minimal with todays PJ's.
If you do decide to build a curved screen make it toroidal not parabolic - there is a big difference! Satellite dishes are parabolic so that all the signals that strike the large reflector are concentrated at the feed horn/antenna and this is why a satellite over 23000 miles away transmitting with less signal strength that a CB radio can be received over much of the North American continent.
Back in the day when people were stamping dishes out of metal someone decided to buff one to a high mirror-like polish and pointed it at the sun. It was discovered that a rod of steel rebar that is used to reinforce cement structures would melt just about as fast as if would fall through the dishes focal point!!!
The moral of the story is: make a large high gain screen parabolic and you will see a really bright image for a very brief time... and then your head will explode! :bigsmile: