As a manager and a contractor, any person who doesn't give two weeks is automatically disqualified from working for me again.
When I was a newbie, we had a guy that worked in my group for 1/2 day, then said he was going to lunch. He never came back. Fast forward 10 years and he comes in for an interview. He looked familiar, when I placed the face, I politely ended the interview and called the company that sent him.
If you don't give 2 weeks, it looks bad on you and your company.