I've come across this on a few forums. Folks seem to think that if they take their car on track then it will automatically be written off/ abused beyond use.
Your fate on a track day is pretty much down to your choosing. If you get all giddy-headed and floor it without knowing a) the track, b) your car, or c) yourself then you are an accident waiting to happen (and the good news is if you don't know all three of the above then you won't have to wait very long

)
If however you come at the event with a bit of caution and sensibility, you'll love it. You don't have to get all screechy with your tyres, and you don't need to be blasting any leader boards. But the chance to get out and give your car some beans in a safe and controlled (and legal) environment is not to be missed.
And thirdly, a few folks often say they'd rather do a track day in something like a Caterham or an Elise. That's great, but the difficulty is you've just thrown a new, unfamiliar vehicle into the equation. Of all the cars I've ever taken around a track, the most enjoyable have been my own because I've been familiar with the vehicle and able to push myself and the car just a little bit deeper.
In short, go on and have some fun! Be careful and you'll be safe. Sit back and you'll miss out!