If there is one piece of fitness equipment - aside from the stepmill - that I think is under-utilized by most gym goers, I would say it is definitely the Bosu Ball.
It is such a versatile fitness tool, I absolutely love them. They can be used to all sorts of strength training, balance and agility exercises, as well as for cardiovascular workouts. Think of it like a STEP, but with the added challenge of an unstable surface. Awesome!
Each year when I go to the Can Fit Pro conference, I try to do at least one training session with the Bosu Ball to get new ideas for using it. Last year I picked up Mindy Mylrea's Bosu DVD workout, but forgot about it until recently.
A few weekends ago I finally gave it a try. It is a lot of fun and perfect for someone new to Bosu training, but I didn't feel the cardio workout was intense enough for me. Unfortunately, there seem to be very few cardio DVDs using the Bosu Ball, which is a shame because it can be a killer workout and, seriously IT IS SO MUCH FUN! Nevertheless, there are tons of DVDs you can buy that focus on strength and core training.
If you work out at a gym where they have Bosu Balls, but aren't sure how to use it, just ask a trainer. Or, if you workout at home, I encourage you to invest in one (you can usually find them for between $100-$140), and pick up a few DVDs to get you started. You won't regret it. You'll boost your fitness and have fun doing it.