Before using this, I was using RadRails, and to me there's no comparison between the two. If you already have Visual Studio 2005 or higher I would highly recommend this, it makes developing RoR apps so much better. I'm not sure if it would be worth getting Visual Studio just to get this addon, but if you already have it I don't think there's another IDE for RoR that's comparable.
Does anyone else know of any other Windows RoR IDEs? What are your thoughts on them?