I use a dual cartridge respirator myself.
Enamels are bad if inhaled, but so are acrylics. Acrylics are essentially plastic suspended in a liquid form, the liquid part evaporates out in the curing proccess leaving a think plastic coating.
Heard about a guy once having to have emergency surgery to remove good sized chunks of both of his lungs because they'd become so clogged and coated with plastic. Guess where it came from. Yep, acrylic spray paint without a respirator.
"Non toxic" on a label doesn't mean fool proof. I want to be around a long time to tell everyone about my plastic airforce, so the respirator is a sound investment that pays for itself easily.
Note: for some hobby applications, the cheap dustmasks don't always help, lots of things can get through them (resin fumes for example) and do you a world of hurt. Respirators, safety goggles and occaisionally latex surgical gloves can be you best friends.