The founder of Friendster believed that the "degrees of bacon" chain was a critical feature. That chain is incredibly expensive to calculate for very large graphs, and produced multi-second page loads. In retrospect, the obvious answer is "drop that feature"; Facebook does fine without it. But Friendster product management thought it was the secret sauce... and maybe it was a reasonable thing to think back in 2002? Dunno, but it sank the company.

Most of what I know about Friendster comes from their #3 and #6 employees (friends).