My 2006 MacBook is still running SUPER STRONG. It runs flawlessly. Only recently have I noticed I need more power since trying to use Handbrake so now it's off to a new 2011 MBP and my excellent 2006 will be the wifes first Mac!
I'm in the same boat. I want to get a 15" macbook pro. Mainly for more screen realestate. But I see no reason I need to ditch my current original core duo 2006 macbook.