Get it from http://www.microsoft.com/downloads/details.aspx?FamilyID=4b106c1f-51e2-42f0-ba32-69bb7e9a3814&DisplayLang=en
This upgrades Office Mobile 6 to 6.1, which allows you to read and edit Office documents created in Open XML format (observant readers will note there's nothing about creating them, but that's not such a biggie).
They've also thrown in the ability to view and extract files from .zip folders - which makes sense since Open XML documents are stored that way.
You can also view SmartArt in PowerPoint Mobile if that's the sort of thing you like to do.
This is a welcome development: Microsoft couldn't really afford to leave this one until version 7, given that the dreaded, revered, firstborn-sacrificed-to iPhone apparently supports Open XML already.
Wouldn't it be nice to have a few more actual WM6 devices in our neck of the woods? Especially from say, oh I don't know, Telecom and Vodafone?
(via Jason Langridge)