Very recently, Microsoft went public with their blogging tool under development, "Windows Live Writer": http://windowslivewriter.spaces.live.com/

Due to MS's pervasiveness and the tool's ease of use it has the potential to become a wide-spread blogging tool.

The developers call:

" Writer is a great client for Windows Live Spaces but also works with other weblogs including Blogger, LiveJournal, TypePad, WordPress (and many others).

Writer supports RSD (Really Simple Discoverability), the Metaweblog API, and the Movable Type API.

We want Writer to work well with every blogging service out there. If you can't get Writer to work with your blog, we want to know."

This might be a low-hanging fruit for providing a well-supported and well-developed Microsoft Windows blogging application compatible with Confluence.

I suggest to give input to the developer team of Windows Live Writer to use the Confluence API for blogging.

Even if there is no direct MS support for a Confluence API, you might want to contribute a Confluence plugin...