One of the biggest "concerns" is creating websites that work on the proliferation of mobile devices. I would guess that, by the time Santa has done his rounds this year, there will be more people surfing the net using them than computers.
I know its going to take a while for the rest of the manufacturers to catch up but you really need to see how bad a lot of images look on the new Macbook Pro Retina. Go to the nearest Apple store and take a look at some sites on one of these machines and you'll see what we're all up against.
I think its time for a new super-image format - or maybe there is one?