As pointed out by Mehrdad you flag his posts. The Moderators do not act on users based on a single insident, and we don't always have the time to go through the person's history. We do some basic checks to ensure it's not a sock pocket account, and if there is discrepencies in voting.
I have previously stated this but will again:
Please flag every discrepency you see. We cannot act upon users or accounts without a track record of irregular activity, and banning users based on a single post, without informing them via e-mail is frowned upon.
Apart from blatant spam accounts there is a fairly strict policy with the moderators around dealing with any users, and we are only allowed to take action based on track records and proof of violations. With voting it is hard, which is why there is scripts in place to revert and handle serial voting, and processes have been put in place to deal with gaming, including a time limited vote reversal period. These we cannot monitor or act upon.
Be detailed in your desciption. If you have more to say then the comment, e-mail a moderator directly, their details are available on their profiles, or otherwise mail team@[relevantsite].com. Jeff will then deal with it or pass it on to a moderator if required.
TheTXI expanded a bit on what the moderators can do with this in his answer here