It's funny that even after all these years and all this money invested in technology, we still haven't come up with anything better than word-of-mouth for hiring great people. Many serial founders have said that, despite the most stringent interview processes and the most sophisticated filtering pipelines, they still have a higher hit rate with people they've worked with in the past.
This isn't to diminish the whispernet. Rather, it shows just how many important signals cannot be quantized.
True, I have found it to be valid as well