But hold on, didn’t I mention one week is not enough for a candidate to be productive and effective? Yes! And that’s why most places have a three-month probation.
If I had to change jobs, I'd be MUCH more comfortable taking a week's vacation, doing a "trial" week, and then making a decision than I would making the decision and then being subjected to a three-month probationary period.
The trial weeks let's both parties dip their toes in the water. I think for many employees, it reduces their risk quite a bit. If it doesn't work out, you're out a week's vacation. If you're three month probation doesn't work out, you're out of a job altogether.