Two Mad Penguin interviews with OpenOffice developers discuss the importance of open data formats.
Gary Edwards explains why clean XML (or an open XML format) allows an organization to avoid being locked into a vendor's solution and then being left high and dry when that vendor goes belly up. Florian Reuter describes using XForms for OpenOffice's forms and the difficulties in writing importers for proprietary document formats.
It heartens me to find good arguments for developing open data formats. Data migration is a well-paying but messy task whose complexity is always underestimated.