Yes, I've been through this too. My gut feeling here is to focus on your audience and think about how they will consume and share this information.
For example, how can you make it easy for Dave to walk into his boss and tell his boss exactly why he should hire you!
There's absolutely no reason why you can't put the case-study on-line to allow people to read, or at least scan through the document on-line. AND allow them to download the PDF so that it's easy for them to print, read off-line or share around their team/colleagues.
Having the content on a web page also gives you more opportunities to engage your audience (social sharing, even comments etc)
Where PDFs can really come into their own is where you have complicated graphs, drawings that you just can't scale well to fit on a screen, provide enough context and stay legible!
Oh, and make sure that you've got links in your case-study PDF documents to take you to relevant/useful pages on your website.
If you do decide to go down the PDF only route - please do your visitors a favour and provide a really good extract so that they know what they're going to get. I've downloaded too many case-studies that turned out to be rubbish, irrelevant or just blatant marketing bumpf! (Thinking about your audience first can also change the way your approach case-studies and whitepapers!)
You could get some good press with something quirky!