I've got a Macbook Pro that's over 3 years old. Key things to do, max out the memory, and get a big hard drive. I've had to upgrade both on mine, and I even recently swapped out the wifi card for the 802.11n version to speed it up.
Use the wireless Time Machine, so if you do lose the hard drive someday you won't be devastated.
Also, I'm not a big fan of extended warranties, but for my college kids I always get one for the laptops and they always pay off. Just got a new power adaptor and a battery on my daughters 3 years old Macbook this week.