When tag support was added to WordPress 2.3 a few people asked about having support for it in the XML-RPC API. That seemed reasonable, especially since there was already a patch in trac that only needed a few updates to work. This also addressed my question of how it should be done (via mt_keywords).
Then we started getting really close to the final release of 2.3 and I realized that I hadn’t looked at how Windows Live Writer dealt with the mt_keywords field. The good news was that it already had keyword support, the bad news was that it only supported it if it knew that the blog on the could deal with it correctly. The method that WLW uses to determine blog features (well, one of the ways) is via the wlwmanifest.xml file. If you look at the list for features that WLW supports when working with WordPress you’ll find that the only one not supported is keywords, because at the time WordPress didn’t support it.
Fast forwarding a bit through this story, I worked on a manifest file (and few other bits around it) that would instruct WLW to specifically turn the keywords feature. Unfortunately by the time that all of this was done it was too late to get it into release of 2.3. So if you were bummed that WLW didn’t support the new tag features in 2.3 out of the box that was completely my bad. If I’d realized what had needed to be done sooner then it probably would have made it. Sorry about that.
But there is more good news to add, keyword support in WLW will work automatically with WordPress 2.3.1 (now in release candidate mode) and the future 2.4 version.
If you use WordPress by checking out updates from Subversion you can get support for tags in WLW by updating to revision 6192 in -trunk or revision 6211 for the 2.3 branch. You can also get support for a new or upgraded blog by using 2.3.1-beta1 or higher.
If you host your blog on WordPress.com then you’ve already had keyword support in WLW for some time, so no problem there.