the plastic keys are starting to wear off because of the oil from your fingers. Pretty much all plastic keyboards suffer this but it is more noticeable on your laptop because the keys are black. If I view the keys on my classic mbp at a certain angle, I can also see that keys that are used a lot have that "shiny" look you are talking about.
This is rubbish!
I've had 4 classic MBPs and now a unibody one. There's no doubt that the material quality of the new black keys is FAR inferior compared to the classic silver ones. On my classic MBPs there was no sign of use whatsoever after 6 months (before i bought the next one) of tough use. On the new one, the keys started to wear of after only two weeks! Especially the lefthand Apple key which I use very often (because of all the shortcuts).
And no, it's not grease or oil on the keys, they are simply being polished, smoothed down by my fingertips!
I find this very disappointing! I used to sell my MBPs after 6 months in mint condition for a reasonable price. It will be a lot harder to sell my now 6 months old MBP with keys as shiny as the glossy display.