I used to like being able to read PDFs in the browser, which Scribd let you do, but now the browsers I use (Chrome and Safari) both have in-browser PDF reading that seems to work more smoothly than Scribd for me, so I've switched to the opposite preference. I do occasionally click on it for PDFs that I expect to be large (such as this one) where I just want to skim a few pages without downloading the whole thing.