See De-anonymizing Members of French Political Forums by Dominique Bongard presented at Passwords13 August 2013
Why would we reconsider the Tor proposal? You do realize that if you're running Tor you shouldn't login to any services that know who you are anyway, rendering your point entirely moot. Instead of trying to create drama, why not find a way to make this into a good example question on using Gravatar with Tor. The answer of course is this: Don't login to anything when Tor is running, as you give up your identity as soon as you login.
The point is that you shouldn't be participating as a logged in user on Stack Exchange or any other site if Tor is active. Sure, it hides you, but it's not smart enough to protect you if you shout on the rooftops that Marsh Ray is now logging into Stack Exchange, or any other service -- Gravatar or no Gravatar.
When you're not running Tor, that's a good time to use Stack Exchange, Gmail, Github, your online banking, etc, when you're not trying to hide because, well, you're HTTP POSTing your identity all over the Internet anyway and Tor can't hide you if you're already telling everyone who you are. If you're not logged in, your Gravatar md5hash doesn't show up, so there's no problem. :)
The fundamental problem with the resource you point to is that the folks whose Gravatar gave them away shouldn't have logged into that service in the first place, as it gave them away the moment they typed in their email address and password, even without Gravatar. Again, the use of Gravatar is a moot point in that case as the fact that you logged in shows up in server logs. That's not a design flaw of Gravatar, it's a flaw in how those users were using the system and a flaw in the design of the political forum. Analogy: If you hide in the bushes, wearing a fake mustache and funny glasses, and then yell out "Yo I'm over here and my name is Marsh Ray" then you're going to be found.
The Stack Exchange Tor Q&A site isn't for discussing political dissension, so there's nothing to hide from here and hence no one should be too terribly concerned. If you are, don't use a Gravatar.
Hope this helps.
If you are concerned about anonymity on Stack Exchange there are two basic solutions as others already mentioned: