Replying to College GPA

I was wondering the significance of grades in college. Obviously you need to pass a class to receive credit, but is there a real difference when it comes to a 3.0 and a 3.5? More of what i'm looking for is how many of you older folk have ever been asked for a college transcript by an employer? I know it's important to learn the material, but is it really worth killing yourself to get a 3.5? Of course a high GPA will set you aside from other applicants, but how big is the difference from a 3.0 to a 3.5. I'm an Engineering major by the way, it would make sense for this type of thing to vary from major to major