It is interesting that Microsoft went on the offensive to detail how Windows Phone 7 stores location data and it honestly looks like they have a decent system in place. One thing that is noted though is that this data is not stored on the phone. I know many will think that is a good thing, but I think it is terrible. You want that type of data stored on a device that is within your control, preferably encrypted.
Do you really trust Microsoft to store your location data for you?