Getting your content into XML is just the half of it, if even that. Many enterprises confuse XML authoring and editing with the actual management of usefully structured content and reusable chunks. Chad Dickerson, CIO of InfoWorld, recently had to migrate their site from eBT's old Dynabase to Percussion (both CMS packages are XML-based). He points out that XML has been as "abused, neglected, and misunderstood" as nearly every other enterprise technology. Specifically, according to Dickerson, it's extremely hard to "maintain the semantic integrity of the data represented in your XML as your business morphs and changes..." Meaningful structure takes work, throughout a content lifecycle...
Read Dickerson's piece, "Heaven of XM-hell?"