I love PDFs due to their computability with other OSs. It would be great if selecting text in the document viewer worked more effectively. I am always reading research papers that have multiple columns and when I try to select text it goes all crazy and selects entire columns or does not realize there is a column at all and continues selecting text until the end of the row.
Also, sometimes when I select text to copy it to another location, 8s turn into boxes or Ns turn into Rs. Some weird stuff happens.
I love how there is the ability to select text, but to make it truly useful these things should be implemented.
Lastly, if the default "Print to file" was PDF instead of PS (PostScript), I think more people would find it useful.