Jeff Schneider has a post entitled Hey, Don Box where he asks

All of us in the SOA blogosphere have appreciated your input and insight. However it has come to my attention that Microsoft isn't practicing what they're preaching. I'm hoping that you can tell me that my information is dead wrong.

I ask one simple favor. Start blogging about how Microsoft is using SOA internally.

Don works on a platforms team so he is the wrong person to ask about first hand experience at actually deploying XML web services or service oriented applications at Microsoft. As for whether Microsoft uses services internally, this is all we do at MSN. I'm responsible for underlying platform services that are used by MSN Messenger, Hotmail, and MSN Spaces. The fact that you can lock down your space to distinct people in your Hotmail address book or the people who are on your Messenger Allow List (i.e. who you've given access to see your presence online) are all due to our service oriented architecture on our back ends. This would be a lot more difficult if each of these applications was a monolithic app on our back end.

I'm also responsible for another set of services which are used MSN Member Directory, MSN Groups, and even Windows MarketPlace which I found out recently are going to be used by a lot more MSN properties without them ever having to ping me. When services work the way they are supposed to that's what happens.

To answer Jeff's question, at least with MSN, Microsoft is definitely practicing what it preaches when it comes to service orientation.