One of the cool things about DITA is how applicable it is to multiple types of docs.  Lots of documents can be authored in a topic-oriented way, whether user guides or training guides or online help or ... whatever.

One of the biggest stumbling blocks in moving to DITA, though, is getting everyone to write their topics as kind of "standalone" chunks.  Authors are so used to writing headings with lower level headings or sibling headings that continue from the previous content, that they struggle when told their content has to be self-explanatory and all-inclusive.

One company I'm working with now has dozens of books that they are "splitting" into DITA topics.  The actual splitting of the topics is only going to take a couple of weeks.  The rewriting, however, is estimated to take months and months of author time. 

Their short term solution is to only publish the books as they had been published before, with the topics pulled back together the way they were (so it reads clearly for now).  Long term they will get everything rewritten and kick in the reusability at that later time.

.K.