Ungrateful people. If I take my time to try and help someone, I'd very much appreciate a "thank you" or something similar once things are sorted out. Just being treated like some sort of discount Google search annoys me to no end.
If it's really too much of an effort for you to show even a tiny hint of gratitude, it's most certainly going to be too much of an effort for me to take my time to help you out in the future.