Windows Live Writer was released this week, with new versions of all the Windows Live applications. I've been following it in beta for over a year. However all my attempts at using it with b2evolution have not been successful enough to use it for my general blogging.
Metaweblog seems to be the most stable API, using Wordpress, Blogger etc, don't even bring up the full list of categories to post to. Metaweblog has some shortfallings, like not being able to delete or edit posts which makes it much less usable than it would otherwise be, it also disables comments, which means I have to go to the web based editor to turn them back on per post, I don't expect anything too fancy like image uploading - that can be worked around quite easily as most client side blogging tools can upload images over FTP to a web site.
Hopefully b2evolution's support will improve, it has remained stagnant for too long in this area. These client side applications are becoming more popular, there are literally dozens of different ones now, and even Word 2007 can post directly to blogs. It is something that should be given a high priority to keep b2evolution competitive with other blog engines.
Update: I'm pleased to say Windows Live Writer works great with the 2.4-RC2 version of b2evolution.