And the likelihood that you'll match somebody got a lot smaller. Names have different spellings, phone numbers have different spellings (to say nothing of different numbers), people have multiple emails. You can't canonicalize some of these either.
So flexibility is available, it's just more computationally expensive for the server to do the extra comparisons. The hash calcs use a little extra battery per user, but I'm much happier to donate some of my processor/battery than I am my Address Book contents.
Not all names are simple or even computable transforms though. How do you deal with entries like "Mom" or "Steve," names like "St. Clair" that may be entered dozens of different ways, or non-English names like "姚明" that may have dozens or hundreds of different possible romanizations, anglicizations, francizations, and spellings under any other language?
How much extra battery are you willing to spend, and more importantly, how much effort are you willing to spend running your users' batteries down for something that you'd never yourself use?
> How do you deal with entries like "Mom" or "Steve," names like "St. Clair" that may be entered dozens of different ways, or non-English names like "姚明" that may have dozens or hundreds of different possible romanizations, anglicizations, francizations, and spellings under any other language?
That's sort of beside the point, though. The question is: How does uploading my Address Book information provide a much more efficient or complete solution to that set of problems? I don't think that it does. In each case, you're dependent on heuristics and sometimes those heuristics are going to miss a match. If I were Twitter, I'd happily accept those misses in exchange for hitting the matches where people spell each other's first names and email addresses consistently (for example).
> how much effort are you willing to spend running your users' batteries down for something that you'd never yourself use?
You lost me there. My point was just that for Twitter, my iPhone CPU/battery are an "externality." So while they might spend more cycles doing server-side comparisons on the hashes my phone sends over, at least they're not paying to compute the hash values.
I'm probably out of my territory (I don't have a phone right now[1]), but my first UI instinct would be to allow address book entries to be grouped (or tagged or labelled, the actual mechanism is secondary), and on first request from the app being asked what groups I'd like to allow it access to. Bonus points for the option to create a per-app group and put some users in right there and then.
