If you are making progress with your current workout, I would keep it the same. Instead of changing the excercise change the rep ranges for the exercise. I also recommend that if people are getting bored with their current routine, put in a different exercise to spice things up a bit. Sometimes that little bit of variety is what you need to keep you interested and keep making gains. Just remember: "if it ain't broke don't fix it".

Every 3rd workout for me. i don't get crazy about it though; doing all sorts of weird isolations exercises. i'm talking usually just barbell to dumbbell, or throwing in a smith machine or hammer strength. But i like to switch the order too like incline bench before flat, and front squats before back etc.

Also pick one lift a week to max out either bench, dead lift, squat, clean and jerk.