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For some examples of XML DBs you can refer to:
Also take a look at http://www.saxonica.com/ (Michael Kay's company) for some insight on how XML DB's can be used.
Remember that it takes years for major process cycles to change. XML DB's may not be in the limelight yet but their time is approaching.
The software my company develops can handle most specs so we've dealt with both and I just know that one monolithic schema/DTD presents its own unique problems over a distributed one. The same type of problems exist with monolithic vs. distributed documents (e.g. a single chapter document vs. a chapter as a collection of concepts). It's up for the project to decide which gives more benefit; However for a team larger than a handful, or when maintainability is important I think distributed gives the greater benefit.
Ok enough of that from me.
A good resource for how to use this powerful language can be found at http://dita.xml.org/. As the parent suggested <oXygen/> for XML is a great editor for this kind of work and comes with a DITA edition.
Also as the parent suggested svn is really the best way to go for revision control but a database like eXist can be a great resource management tool for your content while your working with it.