I think there are assumptions being thrown around. We won't know how effective or obnoxious it'll be until we get either more details or see it in action; no need to get worked up.
I agree with this. Microsoft's previous ventures into consumer security applications weren't the best, but Security Essentials ended up being a solid option. I feel like this is an extension of those efforts.
It looks like this is practically the same approach to how chrome stops malicious websites. MS is basically just taking it to the next level and shielding users from applications themselves.
I think it would be a good feature. It just might take time until their database is well populated.