I've noticed an asthetic bug on SuperUser - I'm not sure if it affects any other sites. Basically, I've reached the daily voting limit, and clicked on the vote up button. While an error was received, the vote count and "depressed" image stayed until I refreshed the page.
This could confuse possible users of the site, as they may be left wondering whether their vote was processed. Especially since we're not dealing necessarily with programmers and sysadmins - users who may not be completely comfortable with computers.