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I've had a (plastic) MBP for two years and I don't think I've ever used it when not wearing a watch. There isn't a single scratch :)
 
I suppose it depends on the position of my hands on the keyboard. If I'm just doing light typing, say just simple e-mails or browsing, the position of my wrist avoids my watch touching the MacBook. But when I'm writing code or when gaming, I take my watch off. Otherwise my watch will bump against the palmrest and sides.

So far so good though, haven't had any dents on my BlackBook with a Moshi palmguard.
 
that could be dangerous when the macbook heats up on your lap :p

Hahaha, I found that funny, good call.

On topic though, I don't wear watches, so if I were to buy one, it would be really fancy and expensive (I don't plan to buy one).
Which means, I would take my watch off, so that the MacBook doesn't scratch IT.
 
Kinda learned to take my watch off after I scratched my white macbook on the first day I got it.

But it gave me a dilemma when I use it on travel, since the watch is worth more than my macbook... take off the watch and put it somewhere with a chance of losing it, or have it on and let it happily scratch all over the place.

Fixed that problem with Moshi palmguard of course, so I'm waiting around for the glassbook version to be released.
 
Opened my MacBook for the first time yesterday and my metal bangle went scratching along the surface of the palm rest, eep! No marks but I'm kind of scared to type with anything on my wrists now! I might decide that I deserve to look pretty more than my MacBook does though ;)
 
Have been wearing a watch while using my MBP for the past year, and it's resulted in many, many scratches along the wrist rest.

Will probably get rid of my watch in a short time...
 
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