I remember Acrobat Reader not sucking up to about version 5 (PDF 1.4, circa 2001). Perhaps not too coincidentally, this is about the level of feature support that most non-Adobe readers have.

Only twice in the past year have I encountered a PDF that didn't work in Preview.app. The first was a PDF of my own creation: I was using LaTeX Beamer as an alternative to PowerPoint, and I embedded a 3d model in the presentation. The other file was a two page brochure where the two pages were individual attachments to an otherwise content-less document. (This was stupid enough that I think we can probably blame it on authoring tools making it too easy to use the fancy features and too hard to do the right thing, ie. concatenating the two documents.)

Imho the moral with Adobe/Acrobat and other such cases (eg. Microsoft/IE) is that when a company starts piling up features on their winning horse to take over _other_ fields, they may very well win that battle, but in the long run they'll have such a bloated messy piece of software that they will lose the war.