One of the reason that some places in the not-Stack Overflow-universe don't share that or when someone voted is to help prevent voter intimidation. On Stack Overflow it's probably not as big of a deal because of the sheer volume of the site, but on smaller sites it can leak information that can lead to bad blood.
I propose that we not show who voted until after the election. Yeah, it's a lot of code for a small badge, but it shows that we have peoples' privacy in mind. Otherwise I can know who has voted so far in the election by just looking for the most recent Constituent badges on a given site.
As Luuklag points out, it should not be shown on the user page either as part of this request for the current election. It's fine to show to the user, just not to the not-user.