Recently, I came across talk about the "social agenda of SGML".  Here's a quote (from Jon Bosak):

In other words, the traditional technical and social agenda of SGML can now be realized on a world-wide scale. And what many people in the traditional SGML community already know, but the world at large has yet to understand, is that the SGML agenda now being carried forward by XML is profoundly revolutionary.

Consider what SGML is all about from the user's standpoint. SGML is basically about the ownership of content. SGML says that content belongs to its creators, not to the makers of document creation tools. The alternative that SGML offers has always been very clear: either create your content in a proprietary word processing or desktop publishing format and bind yourself to a perpetual upgrade relationship with a particular vendor, or choose the SGML road and work with vendors whose business case is built on interoperability. XML does nothing to change this basic choice. What it does is to guarantee that the user-empowering, vendor-independent approach will relatively quickly go from a position espoused by a few true believers to the foundation upon which the world will be building its online communication infrastructure. It means that doing the right thing will become the majority view. And this means a fundamental shift in the relationship between the producers and consumers of document creation software.