I'm exaggerating slightly: I imported a PICT version exported from OG, and then asked Powerpoint to convert to a Microsoft Drawing Object so I could edit it inside PPT. This is w/ OG4.1 and PPT2004, OSX4.1.10 .
I played around w/ exporting in every vector format OG can do, and found that PPT has terrible problems when I try to "ungroup" items. I don't know how OG applies attributes such as Fill and Transparency to its objects, but clearly it's radically different from what Office expects. Try it: save a simple diagram as EPS, then import into PPT and Ungroup. The fonts disappear, the colors go nuts, etc.

Anyone have any ideas for a workaround?