I recently got into mountain biking and I've been riding a hardtail on some of the great southwestern Ohio singletrack trails. Last weekend I was able to demo a $5000 fancy carbon fiber full suspension rig for a few hours and I was instantly hooked. However, I always read stories about the shocks on old mountain bikes being "shot" or losing their amount of travel after several years of riding. Is this true even for the higher-end models?
I weigh 120 lbs and would like to get a full suspension mountainbike, but I'd just like to know how long I should expect it to last before dropping $2000 or so.

...Or maybe I should just suck it up and stick with the hardtail.