Coffee Joulies do work, but their effect isn't very strong, and it's nowhere near their claims that the drink "will be ready to drink three times sooner and will remain hot twice as long." In fact, the effect is barely noticeable.
Well, that's terribly disappointing. Like many, I was excited about the potential for these things to radically alter the way I consume coffee. Fortunately, I was skeptical enough to not spend (at least) $40 backing the project; I'm hoping they're making refunds an easy process for their 4,818 backers.