As a developer on Expression Blend, I'm aware of how criminally under-utilized it is in the developer community. I'll grant that in the past this was because it was a) a separate product you had to pay for (and didn't offer much beyond what VS already provided), and b) was ostensibly marketed towards professional designers employed by IT departments and dev-houses. I can't speak for the latter, but designers in IT departments? Rarer than a Technicolor Dreamcoat in Steve Jobs' wardrobe!
That question was not rhetorical - so if you don't use Blend, and you're thinking of developing a Windows Store application, please give it a go and let us know (that rhymes, I'll add), and if you don't use it, also let us know.