In the past I had blogged about a few issues with IE 9 that might have you second thinking beta testing IE 9 on the same machine that you blogged with Windows Live Writer. I am happy to say that with the Release Candidate that came out today all of the know issues between IE 9 and Live Writer have been fixed. If are still having issues with the release candidate and Live Writer or Live Mail please make a comment in this post and also report the issue in the forums.
If you have been using the IE 9 beta it is recommended that you uninstall it before installing the release candidate. Once you have done the uninstall you can find the new version at http://www.beautyoftheweb.com/#/download.
Ed Bott at ZDNet has a great write-up about IE 9 and tweaks you might want to make if you find a few things different from what you are used to in IE 8.