I wanted to upgrade my hard drive from a 200gb 7200rpm to a 320 gb 7200rpm. Was worried about the warranty void since it is not a user replaceable part. Apple verified it for me.
However, blogs convinced me that it was fairly easy and that if you did it right, an Apple tech probably would not void the warranty. So, armed with ifixit.com pictorial directions, the right tools and a $79 new hard drive, I pulled it off. First I used Carbon Copy (sharewared) and cloned the drive flawlessly. Made sure it would boot and then dissected my precious MacBook Pro! Took my time, used the right tools and voila!! It booted up and I made the switch in about 15 min!!!
Data transfer is twice as fast as the old one. I LOVE Macs!!!!