This is a problem. It's not the biggest problem in the world, but it's a just such a dumb, thoughtless, annoying design flaw that it bears mentioning. Apple's doing headphone jacks wrong. Actually, no, everyone's doing them wrong.
In short: Headphone cords almost uniformly insert into the left cup. Some still connect to both, but most good pairs will connect to just one. And the headphone jack on iMacs is on the right side as you face the screen, as do most other all-in-ones (Lenovo, Samsung, et al—though HP and Acer do get it right). That means when you're wearing your headphones at your desk, you've got to either wear your headphones backwards or drape your cord across your workspace.
Again, this is not a Huge Deal. It is a sort of tiny deal. But it's not like they don't know that's where the jack is supposed to go, either. Basically all laptops have the headphone jack on the left side. And for machines that are built with such attention to detail, especially Apple's famously rigorous design team, this is basically inexplicable. So please, Sir Ive, could you take a moment to disembowel someone and make this right?