I find this popup very annoying, and will stop upvoting questions if I have to see it every time I do so. Can you please add an option to disable it?
According to the linked question:
This happens at random a certain percentage of the time.
In essence, this is a Skinner box. The desired behavior seems to be to encourage upvotes and (potentially) encourage sharing of the question. However, the effectiveness of the response depends on the subject (i.e., you) finding the occasional consequences rewarding.
It seems for you (and me) the conditioning is actually of the positive punishment variety. That means that, whether you plan to or not, you will press the upvote less often than normal now that you've made the connection between behavior and response. You may also find yourself anxious just before upvoting.
Why is the popup a punishment? There are several reasons:
Popup window tend to demand user interaction and are most common when the user might have performed an action they ought to reconsider. There are good uses of the feature:
When something does need fixing, it's better to make sure that the user knows about it.—Jakob Nielsen
But this isn't one of those cases.
It doesn't really serve the user, but the system. When I vote on a question, I'm thinking about the quality of the question, not whether I want to "share" it. This feature serves the developer and not the user.
It hides important information and is not dismissed without:
a. reading the dialog box including the URL, which is highlighted
b. finding the word "close" (N.B.: it's not a button)
c. clicking on the word "close"
Until you complete those steps, the popup is blocking you from seeing whatever it hides.
There may be more problems, but for those of us users who are annoyed by it, there should be an option to turn it off. (Or better yet, kill the feature.)