I'll just qualify that a bit. I am a teacher and am forced to teach my graphics units with Adobe graphic products. So I am dealing with PSD files a lot at work. I often take stuff home to mark and, for the most part, PSD files will open and display unproblematically in Gimp. But, things like mask-clipping, for example, simply will not display properly in Gimp. There are also a one or two other anomalies that are present.
However, as I said, it is true to say that most PSD files most of the time will open unproblematically in Gimp