An interesting issue most won't think if is a concept I've coined as "bandwagon voting". Essentially, if the voters can see what the current trend is, they'll vote with it. This could potentially sway elections towards one direction or the other.
This was a big issue in Florida during the 2000 election. The panhandle of Florida is in the Central Time Zone and polls are open 1 hour later than other parts. The state was called for Al Gore while the polls were still open in the more "Red" panhandle area [0] and there were rumors is skewed the results or caused people to not go out and vote since the state had already been decided. [1]
[0] http://www.nytimes.com/2000/11/08/us/the-2000-elections-the-... [1] [1]
You could delay it a little but live updates is kind of a bad idea.
Minutely or hourly updates might be kind of cool but yeah bandwagoning would be an issue.
I see this as a pro not a con. I want to be reassured that my vote was counted correctly. That is way more important to me than keeping my vote secret from anyone in the room.