Like the author said, not having to leave the interface is the best solution.
For example, I like how one can reply to someone's facebook comment through the email program. It looked like Myspace was trying to do this (based on the fact that every email notification had some unique string in the 'from' address).
Ultimately Gmail will have to provide some kind of api for integrating outside 3rd-party messaging systems (eg a plugin or "Lab" for other not just reading but replying to IM messages, social networking site inboxes, etc...), to compete with Facebook's idea of a universal inbox that pulls them all together.
Sunday, February 13, 2011
This post is a copy of my comment on universal inboxes.