Wiki has this function now. This is quite useful IMO as I want to print out one Q&A or maybe all the favorite topics I have collected over the years and then compile them into a book stylishly. Any ideas? Is this doable?
If you want to further format the output of the data, you can use client side scripting to apply different formatting rules. Alternately, get the source of Stackprinter, add a PDF rendering engine on it, use a userscript to add a link/button to each page, and you can skip the pdf print driver.
MarkSchoonover in this post (Stack Exchange and Stack Overflow in eBook Format) announced the conclusion of a project that intends to do what you propose.
As to implement that on the network, I'm not sure if there would be clear benefits in that. Only a very small percentage of questions and answers are really that good to be "stored" as a .pdf archive. This being said, while the network doesn't have that functionality, you can do it youself, using any of the methods Adam and Mark have stated.