It depends what you're looking for.

In terms of journal articles, publishers have been making PDF (and sometimes PS) files available for well over a decade. Sometimes these are fee based, usually at outragous prices, and sometimes they are free. Even with the fee based journals, many universities will provide public access to articles. Certain disciplines offer pre-prints in centralized repositories. In other disciplines, you may find pre-prints on the researcher's website.

I haven't seen too much offered in the way of books. Sometimes a researcher will provide a PDF of their book on their website, but usually not. Sometimes you will find electronic editions that you access through a web based interface.