I'm sure different guys will have different feelings about this.
I've had sex on the first date with a several women and it never made me think less of them or not want to see them again. If anything, it left me wanting to come back for more because it was so good. It just told me that the girl enjoyed sex, found me attractive, and wanted to do it with me.
I know there are guys who are just interested in scoring another notch on their "pistol" and they might be happy to move on after they get what they were after. But those guys are probably going to move on anyway, either before they get what they want (because they are tired of waiting), or after you eventually do give it up.
The only women that I have wondered about being a bit slutty were ones who actually propostioned me before the first date, although it didn't always cause me to say no.
It seems to have become a rule to wait until the third date to have sex. I'm not agreeing with this, but it seems to have become rather common knowledge. A lot of guys might give up on you after the third date if nothing has happened by then, because they figure you aren't interested in a sexual relationship.
