As an impulse buy I've just purchased Yep via today's MacUpdate Promo. I am impressed and so far so good. At the moment Yep doesn't support Mailsmith (my preferred e-mail client) for e-mailing PDFs but he workaround for now is just to drag'n'drop a PDF onto Mailsmith so it's not a big deal. I've asked the developers to consider Mailsmith support in a future version.

Until I used Yep I had no idea I had so many PDFs (>2000) lying around. As a university lecturer Yep seems to be an ideal way to organise my chaotic PDF collection.