I'm really not bothered about how many partners my girlfriend has had. I only really care that she's been safe in the past. I have a couple of close female friends who are on approximately 100 betwen them, and I've seen men look down on them, or been intimidated by it, and I think it's a shame. Most are just jealous that they couldn't get that many people to sleep with them.
I think with most men it would be an intimidation thing, as in whether she hs slept with someone better than them, or more well endowed etc. I say get over it. My current gf might have slept with more talented lovers, some might buy better presents than me, others know more about DIY, or are funnier. But she's with none of them now.