I don't know if this would be reasonable, so please correct me, but I'd go about it like this:

Nokia has some dealings with facebook, so just make sure that when you set up a facebook app. on say N900 or whatever device the disclaimer giving Nokia access to the personal info is there. Redo this for X number of social sites and pool the data at say OVI. Then you use this data as a basis for interactions, such as girlfriends birthday, stores with music that the person likes (although this will probably direct them into OVI music instead, but still) etc., this will also be perfect for integrating with the GPS/Maps feature. You then add onto this data with the actions performed by the customer, searches for restaurants etc. possibly autoupdate facebook if you say buy three albums with the same band?

Now even I feel that this is invading quite a bit on my privacy, and as I've stated before I live in China so I know something about the subject (btw, they should probably include renren wang as well for us china-dwellers). But if you want a device that acts on your likes you will have to tell it about them, it's like any good relationship really.

I think the biggest problem will be to get people to set up the account and start using it, this needs to be made ridiculously simple and pain-free, maybe start by using the device number and then tying that to the accounts accessed by it? Assuming of course that people are OK with this sort of thing.