I bought the IS as soon as I ordered my white Macbook, thinking that it would solve the orange stain problem. Did it work? Well, yes and no.
I put the IS on the palmrests and track button as soon as I got my Macbook, but three weeks later, I started seeing the notorious orange/brown stain on both palmrests and the track button. I was pissed! Also, regardless of how well the IS is applied, it still does look kind of tacky.
So I decided to remove the IS. And surprise surprise--when I pulled off the IS, I discovered that the palmrests and track button are still white! So basically, the IS did protect the palmrests etc. from hand oil/grime, BUT the catch is that unless you are prepared to shell out $$$ every month to change your IS, your palmrests etc. are still going to look grimy and stained. That defeats the whole purpose of having IS in the first place. Well, forget that.
I ended up getting a white Marware palmrest which I'm liking a lot. The Marware white matches the white on the keys and on the glossy hinge and surface of the Macbook, so it doesn't look bad at all. Also, it's quite comfy because it is soft. The only thing I don't like is that it doesn't line up perfectly with the trackpad and the grey Marware logo on the top left, but I will take that over orange/brown palmrests and cheap-looking reflective plastic any day. All in all, I am very happy with the Marware and wish I had not wasted $50 on the IS.
On a side note, there was some slight residue when I removed the IS. Like the other posters said, you can easily get rid of it with Magic Eraser, or even just your finger (not nails), but you risk getting the little white scuffs that a poster complained about on another thread.
Hope this helps!