Eibach lowering springs, 50k street and track miles and the oem's are still in functioning order.
As others have pointed out, the oem suspension is perfect for long term track use. In other words, you won't blow them on 5 track events.

 

[media]http://www.youtube.com/watch?v=vm95GTX9S6Y[/media]

OEM suspension at 160,000 KM, (~100,000 miles). Plus 1 summer of autocross and 3 track days.

Definitely lacks damping. It tends to bounce off the bumpstops twice after every big curb hop - once on landing, and once after that, too.

As others have said, it depends on how hard you're pushing, too. For 8/10ths driving, they're fine.

 

There's nothing wrong with it from a reliability standpoint. Most tracks are smoother than streets, anyway. If you have super grippy tires, you MIGHT start hitting the bump stops during turns, which will result in strange break-away behavior at the limit of traction but still probably won't damage anything other than your pride.

 

My car has about 80k on the clock and is still on OE suspension with about 26 track days on it and going strong. Ill agree with Travis in that when you really start pushing it the car takes longer to regain composure and on tracks with choppy pavement it might require significantly more courage, but it will definitely teach you more. Sway bars DEFINITELY help with OE suspension.