There are two new videos posted to Channel 9 about VSTO Second Edition, one from Thomas Quinn an architect on the VSTO team, and the other from Martin Sawicki, program manager extraordinaire.
Also, a small comment on VSTO Second Edition. Some have assumed that VSTO second edition is a super set of VSTO 2005 as the name kind of implies. This is not the case. You will want to have both VSTO and VSTO second edition installed at the same time in most cases. VSTO has the document projects for Word 2003 and Excel 2003. VSTO SE adds application add-ins to target Office 2003 and Office 2007. The two products should be installed together to get both document and application level customizations.
You will also note that there are no "production-quality" Office 2007 document level projects available yet. You can get beta/alpha level Office 2007 document projects by trying one of the CTPs of the Orcas version of Visual Studio. "Production-quality" document level projects for Office 2007 won't be available until the next version of Visual Studio ships.