It works, but I'm limited to basic text entry. No fancy HTML was harmed in the making of this post. You can include images, which is something I guess. I would have liked an app that let you enter in HTML markup using something like markdown.
On the plus side, the HP keyboard is nice way to enter in extended amounts of text on a touch only device. Most of the keys work. The media keys work just fine, but most of the TouchPad specific keys are ignored. With the exception of the search key, that invokes the iOS search box. For $20, it's a good enough BT keyboard for my needs. It's HID enough.
I went back and edited this post with an app called, BlogPress. It's not Windows Live Writer, but it's good enough for posting from a tablet. You can do some basic HTML formatting. It's a bit quirky, especially when scrolling at the bottom of the page. The text looks like it's dropping of the bottom of the page and you have to drag the page back up. But it works.