Moderators can add notes to use accounts to tell one another to keep an eye on their behavior. In extreme cases, accounts can be suspended or deleted by moderators as well.
So if you see someone who deserves a "bozo" flag, by all means flag their posts for moderator attention and explain why. If there's a trend forming, moderators can take appropriate action.
In the end, though, down-voting a question/answer that you think is poorly written, not well explained, or too basic to be handled here (i.e. your example of
echo get_post_meta()), is definitely the preferred way of handling this. Users with significant numbers of down-votes stand out and can be easily ignored. It also serves as a not-too-subtle reminder that they need to improve the quality of their posts.
But using an ignore script, I think, is counter productive. If the people who care the most about curating quality on this site hide and ignore the lowest-quality content from their browsers, it makes it that much harder to downvote a bad post or notify a moderator when you see something out-of-whack. When new visitors come to the site, they should see quality and the passion in the community behind maintaining that quality (seen by a clear separation between good and bad posts).