I think that it is totally legit to take the number of sexual pertners someone has had as a valuble source of information about their personality. Dosn’t mean that something is right or wrong, but it does give you insight into how they think about things. If the way they think about things is the direct opposite of how oyu think about things, well, that is a warning sign at least.
For example, to me a person who has had 50+ partners in the last five years is someone who is really interested in sex. This is someone who puts sex pretty high on their priority list. You have to work to get laid that often by that many people. It becomes a hobby in itself–you gotta go out and meet people all the time. That has to cut into the time you spend reading, the time you spend on the SDMB, the time you spend writing, etc, etc. And to me that is a turn-off. I mean, I like sex, but I don’t like it enough to sacrifice all my free time in order to ensure that I’ll get it. To me, a person that dedicates that much time to meeting sexual partners must find sex more enjoyable than almost anything else, and that is simply too differenct from me for me to ever establish a relationship with such a person.