"Modded down" means voted down?

Yes. Oh my. Years later, i am still using Slashdot lingo. :)

How do you want to know about these sockpuppets?

I do not "know," but it is a strong feeling. It is based on proximity of their attitude towards a person or post and the time between the downvotes. There are other hints when some people post anonymously, but their wording style gives them away. On a related note, someone, from time to time, follows my posts and downvotes everything i post up to 3 times. He does it in bursts. The best part is, i love it that someone cares. :)

Creating efficient sockpuppets which are not discovered by a database lookup is IMHO quite difficult.

Wouldn't that depend on how many servers you have.

I'd try to restrict the multiple upvotes to 10% of ones quota. Like this you'll need at least 20 votes (Chaplain) before being able to.

I don't see this "scratching" problem, but who knows.

You can do a simple test, as you are well known and liked. Create a new account. Post something silly only mildly relevant in SoPW (or how it can be done in another language or environment.) Wait a few days. Post nearly the same comment under your own account. (Or reverse the order.) Chances are, under your own name you will be voted up and cause a chain of other responses of a similar grain.