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You gain 1 XP for each node you post that at least one person up-votes.I'm not sure I like this one or not, but it will definitely increase my XP a lot, because I write lots of short comments which very few monks even read and vote on.
No, it won't increase your XP even a whit. The only change on that part was making the documentation clearer about what was already the case.
I really don't like this change. Not only this punishes downvotes, but it also has a discontinuity at half-half upvotes and downvotes
No, the function is actually continuous around zero. If $voteavg is close to zero, then your odds of gaining/losing XP are also close to zero when you cast a down-vote. If the chance of losing 1 XP on very rare occassions is so abhorrent to you, then you are a bit of a hypocrite for dishing out half of your votes as down-votes. The net XP impact for you of casting 1/2 up-votes and 1/2 down-votes would be positive in the long run. So there is no net punishment for 50/50 voting.
Since xdg noted that s/he missed the $voteavg factor in the equation for the odds, then perhaps you did as well. So the standard documentation needs to be expanded to not just show the math but also to explain more clearly what the impact of that math is.
I'm not terribly surprised that one "doesn't like" the chance of getting back a small fraction of what they dish out on occassions when the negativity temporarily has the upper hand. And I appreciate you being honest about it. I'm in the same situation. I have been more likely to cast down-votes than many monks in part because I would sometimes cast what I consider "compensating" down-votes (this will likely change somewhat).
which someone like me might want to work around by casting meaningless upvotes to bring the vtavg over zero.
Yes, the system can't stop people from taking the moral "low road" and trying to game the system. I'm sad that you would choose the moral low road to avoid getting back a fraction of what you dish out. But the game that you are proposing is complex enough that I hope that most people would abandon that game eventually. "PerlMonks: The story of how I learned to stop worrying and stop loving my XP and embraced voting the node honestly". Wouldn't that be nice? I suspect that even you will be tempted to not completely waste the up-votes that you cast just to prevent your $voteavg from temporarily dipping too low and so (I hope) you will tend to up-vote the more deserving of the nodes conveniently at hand. In fact, I would think that the personality that casts a lot of down-votes may find it particularly distasteful to up-vote nodes truly randomly. So I'm not convinced this particular motivation to game the system is that strong in the end.
People very often dislike change. And certainly many will dislike change that takes away a reward that they have come to take for granted (not much complaining on that point this time around, though). So, of course, many will dislike a change that may give them a "punishment" (no matter how small, it appears). I am "lucky" in that the vast majority of my "audience" hardly ever down-votes so this chance of "punishment" only impacts quite a minority.
I presented some of the cases of abuse that motivated these changes. I didn't otherwise try to convince those about to risk punishment (being holier than thou, of course) that this is a Good Thing™. In replies I've noted that this risk is quite low and, in the cases of the counter arguments presented, the "punishment" would also be quite small. But I really don't think anything that I could say would convince those about to be "punished" that the punishment is a Good Thing™. But I think discouraging some fairly common and serious "abuse"1 is worth the minor discouragement of some less abusive activities that are still a disruptive influence (if you are casting half of your votes as down-votes, then you are surely downvoting for relatively minor infractions, the type of thing that leads people to mutter "what was worth down-voting about that?!").
1 I only use the scare quotes in that case because most of it isn't officially defined as "abuse" by site policy, although I think most would agree that the vast majority of it (doing nothing but down-voting tons of ancient nodes by a single author) qualifies as at least a mild form of abuse that is pretty clearly against the spirit of our little system.