Reason I ask is my sister jumps in and out of relationships and trying show her not "everyone" sleeps with the other person in the first week... so how long do you wait in a new relationship before taking a trip to between the sheet?
If by seeing them you mean dating? Typically I start sleeping with someone before we start dating. But typically we have been friends for about a year or so before I'm comfortable sleeping with them. I like this way of doing things; we get to know each other as people first, and then as sexual partners, and then romantically. In a typical heterosexual relationship you have to force a romantic commitment before you even really know them as a person, which I think is totally crazy.
Anyway, no, not everyone sleeps with someone within a week of meeting them, it usually takes me a year or so to get comfortable enough to do that, however there is nothing wrong with being ready within a week. We all go at our own pace!
Totally depends. I've slept with people on the first date, while with others I was seeing them regularly for a month or two and never slept with them at all. Current boyfriend I slept with on our fifth date. It felt right.