Well, just the other day I was watching an American movie and this sentence came up "I should have saw that coming".

So, how often do you hear this kind of usage?
Ahhh! I hear it often enough that it makes me wish that the ghost of the English of whoever said it would rise up and scare them into correct usage!

It's right up there with "I seen" in terms of things that make me wonder if my countrymen enjoy being seen as illiterate.

I don't hear it at work, and God knows I don't hear it at home, but I do hear it on the news when they are interviewing ordinary people and in the crowds at amusement parks and other places where you'll have a mix of social/educational classes.
I agree totally with GG.

I hear this more and more in films and in the news. It has the same effect on me as it does GG and my countrymen are just as guilty.