Safari & PDFs
I didn't like the inline support for PDF reading in Safari 2.0, so much so that I ended up turing it off. When I upgraded to Safari 3.0, I kept reading about the improved PDF support, but every time I opened one with the browser, it complained that it couldn't find an application to show the PDF. So I'd save it on my hard disk, and open it in Finder.
The root cause was two issues. One was an installation of the Adobe PDF reader (which is horrible) that I'd partially deleted; I had to find the AdobePDFViewer.plugin and remove it. (It was in /Library/Internat Plug-ins, which for some reason I had a hard time navigating to in the Finder, I ended up using Terminal to figure this out).
The second was that I'd used a command line call to turn off the inline PDF viewing capability in Safari, and this carried over after I installed 3.0. The command to turn inline PDF viewing back on in Safari is:
defaults write com.apple.Safari WebKitOmitPDFSupport -bool NO
This, in my mind, is an excellent example of the compromises you make when designing a UI for simplicity. Safari has a much smaller set of choices available in preferences than other modern browsers; this key preference is not accessible by UI. In my particular case. I find that incredibly annoying. Of course now that I have inline PDF viewing working again, my overall satisfaction with Safari/OS-X goes up.