I have noticed some down-voting on my questions that haven't been asked recently, but a while back and they seem to be in succession. Just as there is a penalty with too much up-voting, what about suspicious down-voting?
There is an automated system that is on the lookout for suspicious voting, whether up or down. My understanding is that the exact workings of the system are kept private, so as to prevent deliberate workarounds. Regarding your specific situation, note that the votes you received on 2012-08-12 as indicated on your user reputation page are grouped by type of vote rather than by timestamp. So you have 7 upvotes listed in succession, and then 5 downvotes listed in succession. But if you look at the times on these votes, you'll notice that you received votes in this order:
10:04 - up 10:05 - down 10:09 - up 10:10 - up 10:13 - down 10:14 - up 10:15 - up 10:17 - down 10:18 - up 10:19 - down 10:21 - 1 up, 1 down
If we assume for the sake of argument that all of this voting is by one user (which isn't a given, but also isn't too unreasonable since these votes occurred close together in time and all on different posts), then that user voted up 7 posts and voted down 5 posts, netting you +2 in votes received and also +25 reputation. So I don't think there's too much to worry about there.