it just comes down to: if your machine has a problem, do you fix it or replace it? Unless you replace it, EVERY time, get Applecare. Pays for itself with the first repair. If you're really tight with cash, I agree you can hold out until the end of the first year - when I buy a new machine, I just put its Applecare anniversary in iCal as the first entry.
With the exception of Dells (and Apples), pretty much any non-trivial (hard drive, RAM) failure is a mess to get fixed even under warranty - you either have to give up your machine for weeks, or deal with the likes of the "Geek Squad"... Neither of which is a very good experience.
If you value your time at all, or use your machine to get paid, get the Applecare, period.