Hi. Great place to make a first post.
I think the question itself is a little too broad to really answer, being that it wholly dependent on the person. It's interesting to see how many people are cool with multiple sex partners here as opposed to people on the exact opposite end of the spectrum.
For me, I guess it's more dependent on a few thing. If I'm in a relationship with the person in question: if she's clean and I know that she cares for me, it really doesn't matter. I've only slept with two different women, so I'm aware that chances are who I'm dating is gonna have a higher number than me. Which I am wholly OK with because a woman who knows what she likes in bed is insanely hot.
To address the "don't ask/don't tell" deal, I think that those kinds of secrets are detrimental to a relationship's health, being that relationships are about openness. I'm not really a conservative person, so I'm not gonna shun my girl for saying that she's been with X amount of partners. Of course, if it's a super high number I'll ponder it a little bit, but as long as she's clean and we care for each other, it's all good.
Besides that, I'm not really the hypocritical type: if I weren't in a relationship, I'd be trying to bang as many girls as my morality would allow. Now, as far as casual sex is concerned, I don't think that the number is important. Because there isn't really any meaning behind the act; it's just good ol' spontaneous sex.