Is the implementation that's shady/spammy? I don't see how Intro isn't useful for recruiters to instantly have the linkedin profile of the person their emailing available to them on their phone. That way it's a quick reference check.
The spammy part: They toss LinkedIn ads on your emails to other people after you hit send.
The ads bit is a bit shit though.
http://techcrunch.com/2013/09/13/ark-is-like-a-rapportive-mo...
So while Intro seems to have less friction, you have to give up privacy (HAH. Email and privacy always makes me laugh) to achieve it, which does suck.
Shame there wasn't a cooler way to try and handle it by only using headers or something, rather than MITM the whole damned email stack.
Ark is neat though. Out of curiosity, how do you handle double notifications? As in, I get a new email, now I've got a notification in Mail and Ark? Or does Ark replace Mail entirely?