Dropbox keeps a history of file changes for you, optionally forever (costs more).

As for how much of the file is copied in an S3 version, I don't think that's clear. I suspect that's an implementation detail that they aren't sharing. That said, I'd be surprised if the versions were full copies on disk.

If that's the case, then wouldn't http://<domain>/.well-known/finger provide a list of finger URLs? Something like:

{
"finger": "http://example.org/joseph",
"finger": "http://example.org/matt",
"finger": "http://example.org/andy",
"finger": "http://example.org/mike",
"finger": "http://example.org/barry"
}

and so on? Or perhaps I'm missing something. But if that is the case then that list seems backwards, the entries should look like

"joseph": "http://example.org/finger"

Really though I think we should save clients the extra request by default and optimize for the common case. I think you could still maintain the sort of flexibility you are looking for by providing a field that indicated if this was a list of finger URLs.

Could this be made even easier? Why couldn't my JSON services document be at:

http://<domain>/.well-known/finger/<local>

Where <local> is the local part of the email address (just as you suggested for http://example.org/{local}).

I always thought LDAP looked funny, must be all that X.500 influence :-)