You mean, if you replace it yourself, you would void the warranty or not?
As they printed it in their guide, which comes with your Mac if you buy it (I got it with my 17" uMBP and also did it myself), it is safe to assume, that it does not void the warranty.
But as there is still uncertainty in the Mac community and even with Apple support itself, maybe ask them via telephone and email.
The more answers you get (official) the more confused you might get though.
They are replaceable. If you are worried, save the drive that came with your machine and replace it with it (original drive) if you ever have to bring the macbook in for any service. It is very easy to switch out the drive. Good luck! 😀
hey there. i hope this reply helps. Although i own a "novice" macrumors title, i've done quite a bit of hardware replacement with apple notebooks. regarding your question, i own a 13' mb which i wanted to increase performance by upgrading the hard drive. After much research i found that the best replacement was without a doubt a HDD made by western digital called the "black scorpio", which comes in various flavors but overall has the best reviews. the one i put in mine is a 250gb spinning at 7200 rpm with 16 megs of cache. click here for more info: [ http://www.wdc.com/en/products/products.asp?driveid=478 ]. It's as easy as turning everything off, popping the old one out, putting the new one in, fire up the computer, insert original OS disc, and reformat/reinstall your OS. Personally, i'll testify that performance difference was great, and not just in a few areas, my entire system is much more responsive. I also see a huge difference in bigger system commands like copying large (>10gb) amounts of data from one place to another or to an external disc (if it is also 7200). As far as for the replacement process, if your nervous hop on youtube. There's loads of great walk-throughs. have fun!