I've straightened mine once to stick-straight. And it was just for a halloween party in high school (Cleopatra isn't usually pictured with straight hair.)
More often, I'd just change the curl with hot rollers - gave me gorgeous fat curls, and it was a nice change of pace. I have really thin hair, and don't look good at all with it straight and flat. (And booorrring.)
So basically, no, there's no way in hell I'd screw it up by straightening it permanently. It took me many years to figure out how to make it cooperate, and now that we have this understanding, I love my hair... Even though I don't have much anymore. I've got a short little pixie do at the moment, and I LOVE it... but I only love it because it flips out and curls in all the right places. And it's really, really easy to maintain, given how much I'm working these days.