Honestly, if said data is used to generate some demographic profile in order to show me less irrelevant ads while still paying for these incredibly useful services, I don't terribly mind. Advertising has been around for a while but being able to guess what might apply means less reliance on sheer volume in order to get the same value from the "ad space". I completely understand the ways this can backfire (shadowy three-letter agencies stealing that profile info, leaks that reveal info that someone figures out how to tie to your identity, etc) but those things are already distinct possibilities with credit card companies, email providers, loyalty cards, medical records, and a host of other things. Leveraging information to create valuable services that would otherwise not be possible is probably not going away anytime soon. At least this way it's easy to split bar tabs or cab rides.