I love mine too! I stay up way to late doing homework and sometimes I need just another hour to finish something. I pull out the Wii and do some stretches and I set to go a bit long.
My favorite is the balance with the penguins! The one where they kick the soccer balls to you is so hard... Those darn heads.... I get them everytime.
Have you unlocked the one where you just sit still? I thought would be so easy, but I find I'm very wobbly!