I've been talking about VSTO v3 and OBA in my TechEd sessions in Australia and New Zealand, but there have also been lots of questions about OpenXML. Wouter Van Vugt has written a great book called OpenXML Explained and I've been giving out copies in my session and in the TechEd Australia Expo Hall (thanks Doug). I've got a box full left, so while stocks last, if you drop me a mail (via this blog's contact page) I'll ship you one (Australian and NZ addresses only).
If you're happy with a soft copy, I've been waiting for Doug to host it on www.OpenXMLDeveloper.org, but I can wait no longer.
I've attached it to this article uploaded it here and I'll take it down from here when it goes up there.
Update - Doug's just announced that it's now up on www.OpenXMLDeveloper.org, see http://openxmldeveloper.org/articles/1970.aspx and it has all of the sample docs available for download too. I've still got a few hard copies left.