Until recently, I used PDFs mainly for sending out formal/final presentations that could not be edited anymore. That has changed: increased use of images have made PPT so large that the PDF format is now my preferred exchange format with clients. At the end of the project we send the source file across.

I purchased Adobe Acrobat 8, but have since then found that Microsoft's PDF plugin (you can find it here) is actually much better:
  1. It's free (too bad for me, I already purchased Acrobat)
  2. It's (much) faster
  3. It converts better, especially the new sophisticated drop shadows of PPT 2007 do not come out well in a PDF converted by Acrobat 8
I have not yet tried Adobe Acrobat 9, maybe problems 2 and 3 are solved by now, problem 1 definitely not.