Okay, so I couldn't resist putting my two cents in on this one.
First off all, the question of "Is it cheating?" entirely depends on you and your beliefs, values, and situation. If you are single, then it is obviously not cheating. If you are dating or married, it does technically fall into the usual description of cheating, however, the term is relative. The idea of having one sexual partner is a relatively recent invention in our society. If you study history it was very common place for men to sleep with multiple women not that long ago (less than 150 years). They don't call it "the oldest profession" without just cause.
The major problem is that our society was really skewed the line between sex and love. We think that the ultimate expression of love for one person is sex, thus, we believe that love = sex. Reality is that I love lots of people I don't have sex with, and I have sex with lots of people I don't love. Sex, at it's core, is a natural human animalistic need. In fact we are one of the only species on the planet that pair bounds with one person. The natural animal instict is to mate with as many as possible.
The point is simply this. I love my wife. And I have a fine sex life with my wife, however, I have very natural and normal urges to have sex with multiple women. I have no intention of falling in love with any SP's and they have no intention of falling in love with me (I hope). My hope is that she enjoys our encounter, however, realistically, we all know it is a business transaction. There is no denying that.
So, I don't feel like I am cheating or at all bad for my wife. She receives exactly the same love from me as before. Am I going to tell her about it? No. I realize that is slightly hypocritical. I actually feel worse about the lying then about having sex with someone else.
That is the way I see it. For each of us the situation will be different