One of the biggest disappointments when searching Google or any search engine, is clicking on a link and then seeing that you clicked on a PDF file. VERY disappointing.
You sit and wait as Adobe Acrobat takes over your CPU and memory to display a document you probably didn't want anyway!
Acrobat is a great tool for documents, but I wish people would post text versions or summaries on their website. I know google offers HTML versions of PDF docs and that's the way to go, but ARGH! I forget to use it!