I recently posted questions about data storage. Got a bunch of good
XML for accounting (or XBRL, actually, a subset of XML) is an 'emerging standard' with AICPA support. So, I would think that an app that supports it would be better integrated, and there are lots of libraries out there to use XML already in any language I'd be likely to use (Java, for starters).
If you read this far and have any ideas, please comment - what is actually wrong with XML as an option between flat text files and a full database for a small application that should scale up, or at least have the ability to be scaled up in the future.
I don't even know where to start estimating the problem scope.