I find that 8 times out of 10, if I've got a song playing and I'm thinking about what would sound good with it, I end up picking something that is in a compatible key. The only time anymore that I make sure I'm checking the MIK numbers is when I want to do the "Energy Boosting Mix" that they describe on the site where you go 2 numbers forward on the Camelot Wheel to give the mix a key change.