I agree that 72dpi is fine for most displays but I would suggest that 300dpi is the minimum target size for printing and I personally prefer 600dpi for printing 8"x10"s, higher if the target is large, like a poster size print.
.... I think you meant "lower
if the target is large"....
Cause when I do posters I tend to work at < 200dpi, sometimes as low as 90 for real large images. It all depends on the expected viewing distance.http://www.sciencecore.columbia.edu/dem ... /6266.html
So from 10 feet away, the smallest the human eye can perceive is around 0.012", corresponding to a resolution of 83 DPI.
Of course this ignores all sorts of things like moireing effects, and such.