I have the moshi palmguard on my 15" mbp and i like it a lot. It protects the palm rest from scratches if you wear watches and whatnot. I've also seen images of the palm rest area develop pitting on some mbps, so i'm hoping that the palmguard does its job in preventing those.
You can't really tell it's there from afar. It has a nice textured feel to it and matches the color of the MBP well.
I have had a Moshi palm guard on every macbook I've owned, and can't wait for one for my rMBP. I don't use the track pad portion, but LOVE the palm rest. Highly recommended. My old 2004 MB suffered from the pitting, so I've used the Moshi on every mac since.