We recently got the ability to upload our own pictures for our avatars, instead of relaying solely on Gravatar. This is all good of course, but it would be even better if we could also switch back to pictures we added in the past as the avatar.
One benefit is less redundancy on imgur, users who keep changing avatars back and forth (and I'm pretty sure there are such users) are just adding more and more pictures on imgur which are the same.
This feature can be also made network-wise, i.e. user will be able to choose picture he uploaded on Stack Overflow as avatar on other sites in the network.