I still have these mails in my inbox. People who I've never met nor conversed with online in my life.
And whether it's sensitive depends on the context. Revealing one's IP reveals their location, and I can think of many cases in which this is sensitive information.
All those things are communication. Comment threads leaking IP addresses is slightly different from email in that you can only reply all, but it's not that huge of a leap.
Unless someone knows exactly how the internet works, getting their IP address via social engineering is trivial. Facebook's behavior was not a big deal, though fixing it was a positive thing.
I still have these mails in my inbox. People who I've never met nor conversed with online in my life.
And whether it's sensitive depends on the context. Revealing one's IP reveals their location, and I can think of many cases in which this is sensitive information.