We tackled this question and then some at the January Central Texas DITA User Group meeting. Sides are available on Slideshare here:

http://www.slideshare.net/annegentle/what-does-dita-have-to-do-with-wiki

http://www.slideshare.net/almondjoy/redbooks-wiki-central-texas-dita-ug-presentation 

DITA’s capabilities are being put to the test with a wide range of adoption contexts with very different requirements. Can it scale from small shops to industry consortia? Can it adapt to new audiences, new content types, new development methodologies?