Zeyad Rajabi has started a series of very useful hands-on posts over on Brian Jones's blog about working with the Open XML SDK. Recent posts include a Document Assembly Solution for SpreadsheetML and Reading Data from SpreadsheetML.
Alex Brown has two posts in the last week on the ongoing discussions between JTC1, SC34 and OASIS regarding maintenance of ODF: The Maintenance of ODF – an Aide-mémoire and ODF – OASIS and JTC 1 Get It Together.
Eric White continues to blog on many Open XML dev topics, demonstrating the power and elegance of Linq and functional programming techniques as they can be applied to common document processing tasks. His latest posts include Inserting / Deleting / Moving Paragraphs in Open XML Wordprocessing Documents, Remove Rsid Attributes and Elements before Comparing Open XML Documents, and a very cool example of Using LINQ to Query Excel Tables.
Maarten Balliauw, like Eric, is one of those guys who doesn't seem to sleep much. In addition to his work on PHPExcel, he has recently completed Open XML indexers for the Zend Framework Lucene Indexer.