That suggestion makes good sense to me. (Thanks for using this thread, BTW.)
You're welcome.
(*) Ignoring someone isn't as frequent of an action as (let's say) sending merit. If someone can make the case that they ignore people at a rate that would be meaningfully impacted by a confirmation dialog, then I'd be curious to hear it. (And in that case, what I'll do is add a new setting to let people disable the new dialog, but I really don't think that additional complication is worth it: having to persist a new setting turns this from a very simple change into something that theymos will have to review much more carefully.)
What do you think of this?:
For people like you, who find popups annoying or don't want such a feature, we can add a checkbox in the popup that would say "Remember my choice" and then you can mark the checkbox and then click on "Yes" so that next time when you click on "Ignore", you are not asked for confirmation unless you clear cookies or something. I'm sure it's possible. 
Can't we take someone's choice from that checkbox and save it as a cookie so that the browser remembers it just like how the browser keeps us logged in forever after we mark the "Always stay logged in" checkbox when we are logging in to the forum? If it's possible, it will probably be easier and will require less hassle than adding a new setting for letting users disable the dialog box.
Are you sure about that? I've seen enough posts from people who can no longer view their Ignore list, because it's too long doesn't load before it times out. Most users haven't sent that many sMerits, and I can only hope people use the Ignore list when they read crap. I know there are many more posts that aren't worth reading than there are good posts, so it would make sense to use the Ignore button a lot.
Do you guys ignore every shitposter? Why? I don't think it's necessary to ignore every single shitposter in the forum because there are too many, and it's almost an unending road, you ignore 100 and there will be 200 more in the next week.
The best way is to ignore such users the way how you ignore people or things in real life, pass by them, and behave and react like they don't exist. Just don't give them attention, don't read their posts, just have a look and move in. You don't need to read the whole post to understand whether it is going to be good or not, having a general view of it or maybe reading a sentence or two would give you an idea and then you can move on.
The ignore button should be used for absolutely annoying users, those that you know are unbearable to see or watch roaming around in every thread in the forum.