1. Back when I could downvote, I voted down a bit over 1/3 of the comments I read, voted up about 1/10, and consciously left neutral the rest. I tried to read every comment. These days, I usually don't bother.

2. no - I think the author of something is important context for understanding it, and I don't really see the point of the 'boo-vote'. And I usually browse in Chrome.

3. no threshold.

4. Everything about a post is a potential influence on my voting. Writing style is probably the biggest determinant for whether something gets up or down voted.

5. I try to keep my subconscious in the basement with my superego, soul, and Cartesian theater.

6. Bad posts get downvoted. Good ones get upvoted.

7. I almost never make comments saying how I voted and why, as this is almost always off-topic.

8. yes to all of the above, except 'reward' and 'agree/disagree'. Mostly to nudge the comment up/down.

9. no limit on downvotes. Also, showing number of up/downvotes, rather than a flat total.

10. If I reply to a comment, I don't downvote it - if it was worth downvoting, then it's not worth a reply. If a comment inspires a discussion, that's evidence it should be upvoted.

11. I don't think I have a reaction to that.

12. A rough characterization of my comment-voting procedure (when I had downvotes):

-downvote if blatantly off-topic, nonsensical, or otherwise really bad (cf. Lojban)
-otherwise, upvote if underrated (a fine comment with a negative score)
-otherwise, upvote if the comment represents an unpopular (here) view that is expressed well
-otherwise, downvote if the comment doesn't add anything to the discussion
-otherwise, upvote if the comment is extremely well-written, along with a good argument, link, or citation.
-otherwise, upvote if the comment is passably good and led to an excellent discussion
-otherwise, downvote if the comment is terribly overrated (not good comment with more than 10 points), especially if it seems to merely state something people here agree with.
-otherwise, strongly consider a downvote and see if it seems like the right thing to do.
-otherwise, leave neutral.