I have been ballroom dancing for 8 years now, entirely by choice. I never wanted to dance at ALL when I was a kid, I thought it was corny too. After I ran across an ad in the paper about learning to ballroom dance when I was 14, I went in for a free lesson on a whim because I felt that my life was becoming boring...and I have never quit. It is very good for your health and your memory, it is easier than you think to learn the basics, and you will realize it's not nealy as lame as it sounds. It can give you a feeling of gracefulness and lightheartedness like nothing else can. ^_^
**Also, one BIG thing to be aware of. No one is looking at you when you are dancing. I promise. You know why? Because EVERYONE in the room is in the same boat as you and just as nervous. Everyone else is too focused on how they look to be concerned with what you are doing. I taught dancing for over a year and I know this from experience.
SK-you should defnitely try swing dancing if you get the chance to! It is such a fun dance, and there are at least 5 different varieties and styles of swing dancing that are commonly danced. West Coast Swing is a favorite of mine. Cool, slick, and not all that strenuous. xD