That's the thing though, I'm paranoid about computers, unfortunatly. When something goes wrong (or seems to have) with my equipment I poop myself!
This Macbook is about 18 months old, is out of warrenty now, and has never done anything strange like this before :s
mine is 12 months old, with 2 more years thanks to APP.
dont stress yourself out over it: i used to be even more paranoid than you, wondering if being a heavy user would kill my laptop shortly after 3 years. have formatted the thing 4 times as well, and well..done a lot of wierd things that would make most people cringe, like toying with the BSD kernel.
but, you know, as long as its working, its working, right? and if it isnt...well...there's always a service centre. although you should have gotten the APP: it'll give you a peace of mind for at least 2 more years.
anyway, think about it: the Macbooks are so cheap nowadays, its just a little more than 1-2 months salary. (that is if i dont give my salary back to mom and dad. ^^
And if you have been frugal and been saving money, then you will have some cash at hand to plonk into when your notebook decides to act up.
(its worse for me: im still a student, so i have to scrimp and save and skip meals so that i can fulfill my dream of owning 2 Macbooks and 1 Macbook Pro. Holiday jobs dont fetch much $.)