I've had my 17" MacBook Pro 5 years 9 months. It has the glass trackpad, it's a unibody model.
I've used the laptop almost every single day since I bought it and I always use the trackpad, I don't use an external mouse.
The trackpad shows no signs of wear at all. It feels the same all over, from the edge to the centre. It also shows no visual signs of wear. No blemishes of any kind.
In my opinion if it has worn at all, it's so small I cannot identify it. Maybe if I had a microscope I could see something.