I hadn't heard Windows was entering mobile, but it doesn't surprises me. I think Microsoft has their own reputation to fight off. Many people think Microsoft OS consume many resources and tries to limit you and force you to only use MS complements. We'd have to wait and see I guess.
I have used Android and I feel okay with them so I don't think I'll switch OS unless I have to start over,. I think many feel like me so MS probably would, at least initially, just have the new people entering to the mobile market while older users will stick to what they know...