Based on my personal observations over the past twenty-five years (my adulthood), which I do not claim is a representative sample, I'd say the actual percentages are probably higher. I'd guess that 60% of husbands have had affairs and probably 40% of wives. I think it grows more common all the time, and it wouldn't surprise me to learn that the growth is faster among women. Again, this is based on my observation. I'm not saying 40% of the women on FR are having affairs, so no one needs get upset.
'Tis a real shame.
MM