Joel Spolsky has a great article today regarding the Microsoft release of the Office binary file format specifications.
Why are the Microsoft Office file formats so complicated?
If you started reading these documents with the hope of spending a weekend writing some spiffy code that imports Word documents into your blog system, or creates Excel-formatted spreadsheets with your personal finance data, the complexity and length of the spec probably cured you of that desire pretty darn quickly.
It’s a good summary and Joel raises some good points about how the file format likely got so complicated over time. He’s also got some good workarounds that, depending on what you’re trying to do, could avoid having to read or write these formats directly.