Yes, a little! I have had a Speck on my 17" MBP for the last year. I always take it off and clean it, let's say, once a month. I took it off to show people how much sexier a 17" looks than a 13" and it had a few scratches where crumbs and what not had fallen into the case and scratched. Most of them rubbed off however. It is important to note that the case didn't scratch the notebook, crap I let fall into the case did.
I still strongly recommend a case like this though, as every other MBP I've seen (and I do see a lot, as a university student) without a case looks 4.2x10^22 times more roughed up than mine. The case will protect against dings and what not, the extremely small scratches are worth the added protection, especially if you're like me and carry your laptop to class.
Also notable, is the case will add around a pound of weight and make your laptop a bit uglier if you make the mistake that I did and get a coloured case for your MBP -I got black. If you get a see through case (like the one offered from Speck) it makes the laptop look much better, as it becomes shiny.
