You're not alone my friend! I'm in the same boat as you. I want a laptop that will have a long lifetime (up to 5 years) while remaining portable and am afraid the upcoming macbook won't be enough.

Still, I could maybe update sooner than that...
Well, any laptop can have a long lifetime (my mom still has a G4 iBook that is almost 5 years old now, and it is still suitable for word processing, etc.).
But when you're talking about 5 year timeframes, any laptop you buy is going to be very outdated in that timeframe. Even if you bought the $2499 MacBook Pro, if your expectation is for it to handle everything you could throw at it in 2012, that is just a bit much.
It all depends on what you mean by "lifetime" though, really. Plenty of people still use machines that are 5-10 years old, but you don't expect to necessarily be able to easily run the latest OS and software.
-Zadillo