I started becoming extremely skeptical of peer review when my employer published what was effectively a press release for one of our products in a scientific journal. One of the "co-authors" was someone I worked closely with, and I don't think a single word could actually be attributed to him; he just signed off on it.

Obviously there's good papers and bad papers, but that was the most egregious violation of the notions of scientific integrity I was taught that I had seen to date. And it's only gotten worse since.