I'll use this posting to experiment a bit. First, if I insert a picture into the document, will that be uploaded and linked in the post? I'll insert the image directly below this line:
Well, that worked! The secret is to choose the metaWeblog API instead of the MovableType API, despite the fact that Google recommends the latter: WordPress supports both, but the metaWeblog API appears to be better supported. I tried using the MovableType API initially; the posting title wasn't carried over, and tags didn't work. Both work with metaWeblog.
This really is excellent, especially because of the image embedding. Now all I want is for Google to add support for Google Gears to Google Docs and Spreadsheets, and I'll be very happy indeed.