I have heard conflicting reports regarding the necessity of painting plaster walls with some frequency. I purchased an 80 year old house with plaster walls and would like to know the maintenance required.
I have also heard that wiping down the walls with water is sufficient but this seems odd - will this get through today's latex paint? Does one not use latex paint on plaster?? Any help greatly appreciated.

There is no set time period for painting walls. Most people will repaint as the need or their whim arises. Some people paint every year, 5, 10 years. Flat latex paint really cannot be washed very well as it tends to remove the paint. This is one reason why you can wash the walls with water. You are actually going to remove some of the paint with the scrubbing. Satin will stand up much better, while semi-gloss will withstand most anything.