I’m not sure how long this has been available but you can now post to your blog using Google Docs & Spreadsheets. You can add your blog by clicking the Publish button. In the dialog your see a button labeled “Post to blog”.
As a blog editor, Google Docs & Spreadsheets is a bit awkward. For instance, to add image from a Web source you have to edit the HTML directly. There is a function to insert pictures from your computer however. One advantage of using Google Docs & Spreadsheets is it does keep a revision history of your document which can sometimes be handy. Also missing are tools to insert tags or blog preview similar to Windows Live Writer. Until there are more blog friendly features I’d stick with a more dedicated blogging editor.
Oops! Looks like there still some bugs to iron out. For some reason, Google Docs & Spreadsheets returns an error about an empty element when I tried try to publish this article. It does not appear to be a MetaWeblog API error but has something to do with the format of the document. I had to finish this post with Windows Live Writer.