Oh man, I feel your pain on the muddy prints. I went through a whole batch of holiday cards that looked like they were done in charcoal instead of color. That tool is a lifesaver. I just make sure to let my monitor warm up for a good half hour before I do any serious work, and I re-check the calibration every month or so. It seems to drift a tiny bit over time, especially with cheaper screens.
My buddy learned that lesson the hard way with some wedding photos. His prints came back with everyone looking a bit orange and he was so confused. A proper calibration fixed it completely.