I'm not sure it's recommended to be resting your wrists on the laptop at all. You're going to injure yourself like that. Every recommendation I've ever seen is to have your wrists in the air so that they're straight and level.
I already have issues with repetitive stress pain when I use a laptop too long. I mainly try to avoid the laptop when at all possible and just use my 8+ year old desktop instead for all work things.
As a plus, it has drastically cut down on the amount of "bonus" work I do at home in the evenings. When the choice is getting a little more work done vs not having tendons that hurt to move for the next 3 days, I'll take the lack of pain every time :)
My physio told me it was incredibly unhealthy to sit in the same position for more than 40 minutes at a time. (His exact words were "I'd tell you to move every 20 minutes but I know what you programmers are like")