May I have your card, Madam?
Solution 1:
Yes, you get one of those cards for every woman you get into bed. Generally there is only one card per character, but there are two characters that have two cards each. Collecting all of them does not do anything besides letting you see them, there is no additional benefit.
These cards are probably the most-criticized aspect of The Witcher. You can try to get them all, but you can also completely ignore that part of the game. They don't have any further effect on the game.