Well, I know for myself: email is enough of a distraction without adding twitter to it. Rapportive provides a useful service by providing me more information about my contacts. By adding the ability to reply to twitter, though, it becomes more than service providing information; It ends up becoming another possible distraction. No, I don't have ADHD. I just have little self control when it comes to things that pull me out of writing. My brain resists work.

Also, of course, there's the fear of inevitable feature bloat. A service that works well at one thing should continue improving in that area without adding unnecessary features.

Way too much sensitive data in my gmail account that I don't want broadcast to the world via twitter. It doesn't matter what kind of controls are in place, I'm not taking the risk that all of my online shopping, password resets, private email, etc. gets accidentally tweeted.

That guy must be really, really, mad. Who would not like "allow access to data on mail.google.com"?