I've taken as long as I want with the two "real" job offers that I've had.
The first one gave me a month to decide. On the last day of the decision date, I called and told the manager that I wouldn't be accepting the job. He asked why. I told him that if he needed an answer that day, then the answer is no. He asked me how much more time I wanted, and he gave it to me.
The second job said I had a week to decide. I told the manager I wanted more time and he told me to ignore the dealine. I then went back and forth on salary negotiations for a couple of weeks after that and we decided on a start date of my choice (six weeks later).
I'm a real pain in the ass to hire.