Re: people's unique advertising ID numbers
As someone with no interest otherwise in MS software my interest was still raised by the above ID business.
If you're an app developer and want to serve adverts in your application or game, you need some way to uniquely identify the user or player (or at least the device your software is running on). This is something all ad-pushers (for want of a better term) require. Most platforms provide such an identifier as part of their API.
For example, iOS provides ASIdentifierManager.advertisingIdentifier, Windows provides Windows::System::UserProfile::AdvertisingManager::AdvertisingId, and I think it's fairly safe to assume Android, and even Blackberry, have something similar (I can't be bothered to look them up right now).