My attempts to encourage users posting to one of my websites to use Gravatar just added one more confusing piece of the puzzle to those encountering the WP backend for the first time. Most didn't bother.

Honestly being able to upload an image for your avatar on a particular site seems so basic outside of the WP world that it really strikes me as the kind of thing that should be in core.

And Gravatar seems like a perfect fit for Jetpack.