speed
I love my Mac. I really can't imagine going back to windows or even Linux for my desktop at this point. But I've got a beef w/ the speed of this sleek little box that I spend the majority of my waking hours in front of. It's kind of a dog.
I recently put another gig of ram into it, which has kept it from the infernal swapping, but for straight-up development work, it's just not enough any more. I'd drop the cash on a new laptop today if Apple was selling something half-again as fast, but they aren't. The clock speed increases aren't fooling anyone. I need something that feels as fast as the thinkpads my friends are starting to tote around in lieu of their PowerBooks.
So c'mon Apple. Get it together so I can spend money with you again.