I prefer waiting. Why? I never know, when I'm going to sell the Mac to buy a new one. Furthermore, why give the money to apple sooner, when I can invest it until then?
when i purchased my powerbook, i decided to wait to purchase applecare until later. to be honest, i just wasn't ready to pony up the $349 to buy applecare at the same time as my powerbook. and about 8 months later, i started checking out ebay and craigslist, and was lucky enough to find an unopened applecare for powerbook package on craigslist for half the retail price. a local student received a powerbook from his parents, with applecare, but he ended up selling the powerbook to get a pc (don't ask - i didn't even want to go there) and didn't use the applecare at all and the person who bought it didn't want it. he was just looking for some quick cash and he didn't pay for the applecare to begin with so it wasn't at a loss to him.
i haven't had any problems with my powerbook so far (knock on wood), but i thought applecare would be good in case i do have problems in the future, and/or if i want to sell the powerbook in the future. at this point, i do think i'm going to put it up for sale early next year - just want to save up enough for a new powerbook (with mini-dvi out) plus a 20" display...
I too waited and got a call from Apple last night telling me that the warranty was up on my Powerbook (since that was a year from purchase). The woman then offered me the Applecare coverage for £199 (compared with £279 on the Apple store and £220 from the HE store). I had meant to buy it anyway so just took them up on the offer.
Worth waiting the year, the cash is as well sitting in your bank account earning interest than Apple's