The big problem is
At the moment this information may be "relatively" worthless.
When google started your data was probably worth a couple of pence.
Now it's worth 10 to 140 dollars or whatever.
How much will it be worth tomorrow and not just in monetary terms.
I read an article somewhere once about reasons we need to fear google and about the only point I took away from it as plausible is this.
At the moment google are riding high on the wave. Lords of all they survey and the data is being used "relatively" benignly.
What if that changes and google is no long cock-of-the-hoop.
As their popularity\relevance wanes, what would they do with your information then?
For me that's the big question.
When you're making money it's easier to appear as the big friendly corp while quietly tearing the arse out people in the background.
However when that same corp has it's back against the wall and is staring a MySpace decline in the face, they will not even pretend to be friendly in any way.
Will they take the hoard of data they have collected and abuse it in any way they can to try and prop up a failing business?
To add something else to that that popped into my head.
What happens to the data when they decide they're too big and powerful to be governed by the law or any particular government?