I'd like to see Apple produce a line of desktops that are as upgradeable as a Mac Pro, but without the workstation-class hardware (more inline spec-wise with mainstream PCs).
I'd like a desktop Mac, but I want to have the ability to change out my video card and processor (if need be), or even just some expansion slots. Don't get me wrong, the iMac is a beautiful design, but is off-putting for those of us that like to tinker.
I've had a few co-workers sold on the Mac, but the mini is too low-end, the Mac Pro is too expensive and a lot of people are concerned that if the display goes out on the iMac, they can't easily replace it.