No doubt in my mind the effect is real — not for everyone but for some. Have seen it among people I know.
I think it is especially likely when a household has two incomes and one person is laid off. When there is still a fulltime salary and benefits, the unemployment check may be enough of a supplement that the laid off person has little incentive to hunt for a job.
When I was young and had no responsibilities, I was laid off from my first big job. I got my next job the exact same day I got my last unemployment check. It would have been the same no matter how many weeks I had.