Hard to say because it depends on the girl, and indeed the man, but I wouldn't automatically think a girl was a slapper just because she went to bed with me on the first night, nor would I necessarily think she was classy for waiting a few dates. It's all just a small part of the composite impression you give him. You can look cheap and easy and never go to bed with anyone, ever.
Just go with the flow and when it feels comfortable, I'm sure you'll know. Enjoy :)