i've not only seen post docs, i've worked with them. i've worked with a post doc faculty member, phd graduates, MDs who after that go into research instead of clinical practice, MD/PhD students, and MS graduates. and haven't found one person who'd say to me "don't do PhD". the only complaint i heard was from the MS graduate and that was, "i wish i was a boy so that i can join PhD instead of preparing for marriage and family." they all are extremely happy. might not be the same case for PhDs and post docs in other sects of life sciences though.