I'm traveling right now and don't have a lot of time to go really deep on this, but today's interoperability announcement is great for Microsoft for a lot of reasons. Gray Knowlton posted on this today, it's a great read if you want to understand how Office and file formats are affected.
Here's an excerpt from Gray's post that is pretty important:
"The change should also underscore the idea that support for Open XML is not the same as opposition to other standards, despite many claims to this effect. Different formats are a means to achieving specific types of work, and interested communities exist to offer support for them. Today's commitment creates new opportunities to use many document formats in Office, and will allow people a greater ability to choose the formats that best suit their specific needs. This is good for our customers, but it's good for our business, too; adding these interfaces makes a lot of sense."
This is a good step forward for us. I hope this gives us more of a chance to work with various technology and user groups, being more open should help folks who want to work with Office.