If you run Windows Live Writer Beta2, and your system's regional settings is not set to en-us, then the spell checker probably won't work.

Quite funny, since you'd probably need that most if you're NOT natively speaking English.

Anyway, it seams that I'm a complete idiot as I haven't noticed a fix that is apparently out there for some time now.

So, if you want your spell checker back, go to that blog post.