Do guys really care about a girls sexual history?

[9th Engineer]

I mean we all have done things we're not proud of

I would judge someone taking this attitude much differently than someone taking the attitude that they had every right to do what they did and don't give a damn what you think about it (which seems to be commonly voiced here). A big chunk of the rhetoric being thrown by Shawnee and the like is that anyone who thinks that a persons history has any impact on the here and now is a bigot and ought to just bring themselves up to date and shut up. That's really the attitude I've been fighting against here.
I believe that everyone is a conglomaration of all past experiences, none of which ever go away and all of which are relevent to predicting a persons future behavior. We got sidetracked for a while on whether or not everyone cares about the predicted outcome, but none-the-less it is there.
Even if you love someone deeply you would have to be a complete fool to disregard their past. Doing so will lead to nothing but heartache and leave you on the side of the road wondering "why?!?...". Love by itself, especially any love less than a decade old and strong, is the weakest hinge on which to hang a commitment like marrige. Like it or not, love does not conquer all. The only place this exists is in fantasy and movie scripts.
In the end, you have to base your choices on what people do, not what they say. We often take that advice in dealing with people in other ways, it also applies to relationships, commitments, and sex.