Jack,
Because you want to keep the computer for 5 years I would say get the macbook pro. It has a faster processor the ability to hold more memory and the graphics card has more memory. The processor is not something you can change out during the time you have it so go as fast as you can there. Moreover, you'll be getting a bigger HD and memory out of the gate so take that into consideration with the price. Consider the refurb as an option as well. Same warranty as new but at a significant price decrease. I've done this twice now with very good success.
Apple Care for the laptop is almost a must but you have up until the original warranty expires to get it and add it to the primary converge. This is 1 year from purchase. You won't need phone support since you can just call me. But if you have hardware problems it's a godsend. I've only used it once but if I didn't have it I would have been porked. Keep in mind that I have had over 7 different Macs in different configurations in the last 5 years and only 1 AppleCare issue. Desktop I wouldn't do it, laptop, without a doubt. Also, you can get AppleCare from anywhere as long as it is apple care. It's just another retail product from Apple. Amazon typically sells it for ~$50 less then Apple and it's the same thing. Don't be fooled by the Apple store idiots.
Geoff,
You and I are getting the new iMac 24" 2.8Ghz once the new Mac OS X, Leopard, hits the streets. This way we'll get the new OS for free. Should be sometime in October.
As for resale. Macs hold their value very well. I have a 3 year old iMac that I plan to get $800 for. I couldn't do that with a 3 year old PC POS. I have sold both Apple laptop and desktop with great success on eBay.
->Ben