Does anyone know whether Microsoft supports or plans to support OpenID?
I am asking this because I need to decide whether or not to use OpenID in my new product, and it's very important to me that my user can use Hotmail.
No, Windows Live ID is not an OpenID Provider, nor are (most) Microsoft sites OpenID relying parties.
Microsoft is still researching OpenID adoption. I expect they will become an OpenID Provider eventually, but no date has been announced as far as I know.