That's not all that matters. IMO the real decision is: do you /trust/ MS ? Do you trust that they anonymize collected data and that they won't secretly change collected data? Do you trust future MS with that information.

Bear with me. This seems like the wrong question, but not for the reason you might expect. Rather, I think that it might be wrong because, even if Microsoft acts in completely good faith, it is damn near impossible to anonymise collected data properly [obligatory citation of the 'anonymised' AOL search data]. It doesn't matter whether I trust someone to do something if they (probably) can't do it.