excellent questions...
i used to work at apple so i know this topic very well.
every new mac comes with 1 year of parts and labor coverage, and 90 days for telephone support.
the 1 year parts and labor covers all the hardware on the machine. it does not cover any physical damage. so liquid damage and "dropping" the laptop are not covered. also, you are not allowed to open the computers. you can upgrade the ram and hard drive on select models, but before these new unibody systems you would have to physically open the macbook pro and upgrade the hard drive.
anytime within the first year of buying your mac, you can purchase the upgradeable AppleCare. keep in mind that the education discount for college students and for teachers will save you lots of money on the applecare of any mac. only within the first year of buying your mac can you upgrade to the applecare. you cannot upgrade after the 1-year.
i find it important to purchase applecare on any mac. it ensures your computer will work for a full 3-years (if you do not physically damage the computer). you have 3 full years of phone tech support (tech support out-of-warranty is very very expensive). also, if you plan to resell your computer after 1 year, people are way more interested in buying it if it is covered under apple care.
i'd recommend applecare for anyway. i haven't had any terrible experiences after the 1 year. hope this information helps. also, if you wait too long to upgrade within the 1 year, you can run into trouble. you can register the applecare over the phone or the internet. but if you order the box online for applecare, you have to wait for shipping, etc. so try not to wait until the very last minute! i did that once before and i wasnt able to call in until the next Monday (weekend you can't register if i remember correctly).