I've been testing this myself now on a couple of comic panels. You can get feedback real fast, but one problem is the hive mind mentality that will occur. The more downvotes you get, the bigger the chance that more people will give downvotes or not vote at all. And if you get upvotes fast, people will join in giving upvotes, thinking that there is something brilliant going on, even if they don't get it.
That's why cat videos rule Youtube and the reason Donald Trump could be president one day.
Edit: This sounded a bit negative. My experience with imgur has been a positive one, and I do think you can use it to your advantage if you understand how the game plays out.