Cliff, agree with your point about the potential for behavioural understanding. However this doesn't require real time tracking. Checkins are already enough to start giving users very valuable feedback about places they might like based on where they and like minded people have been.

There is a frequent complain about checkins services, that, aside from knowing where your friends might be, they deliver little value, but this should change soon.

Having the ability to predict places one might like is also a marketer's dream. Everybody talks about the potential monetization of these services but knowing that one user is near a shop isn't good enough and prohibits any sort of push marketing, as users would be swamped with irrelevant offers.

Knowing that someone who might like your business is nearby is game-changing, because your chances of conversion are of a different order all together. One might say that if done really well (predicting the right places), you might even start considering push mktg (as signal/noise ratio will be good enough).

Cloud based recommendation engine for locations is what we do at http://www.LikeCube.com. Any web/mobile app capturing user location and who want to experience these benefits might want to contact us.

Sure, this may be too much for some users, but others will relish the automation.

Think about it, the behavioural understanding that can then be derived from knowing/tracking actual data rather than when/if someone chooses to announce their presence.

However, as with all these comments, Point 1 can be extended from '…will suit some brands more than others' to '…will suit some brands and users more than others.'