I have noticed a gradual increase in the use of Adobe's Portable Document Format (PDF) on websites. I saw that the NHL had abandoned the rest of the season, so I went to the website of my local hockey team to read the news. On the front page, there was a link to a letter from the NHL's Commissioner to the hockey fans. Clicking the link sent me, without warning, to a PDF document of the letter. It was a 1-page letter that could easily have been produced in plain old HTML.
PDFs suck, people! They require the Adobe Reader plug-in to be accessed (which may not be available for your user agent), take an age to load, and never fit in with a website's design. They're great for huge user guides and technical manuals, but they're a fucking pain in the ass otherwise.
So please, web designers, tell your clients that PDFs should be used as an absolute last resort.