Well mine has stained, but at a very normal rate. I mean, what did you expect on a white/grey laptop? My hands aren't spotless every time I use my MacBook. In fact, I can't even see the stain. My friends had to point it out, and this was only noticeable under certain lighting. It wasn't a big issue.
And today, I used a general purpose spray cleaner and wiped the palmrest area with a tissue. I think it's clean, but again, I couldn't even see the stain before. I'll ask a friend later.