Upgrading a MacBook Pro
Having already put a 7200RPM drive in my MacBook which I've now given to my father, I decided to put a 320GB, 7200RPM drive in my new MacBook Pro, along with 4GB of RAM, and it's made a substantial difference (my XBench scores after the upgrade are included).
For 2 years I had a black MacBook that was my primary Mac, and towards the beginning of the year I upgraded its internal hard drive to a 100GB, 7200RPM one, which made a substantial difference in terms of not only raw speed but also responsiveness. The decreased seek time of a 7200RPM drive can make huge difference in productivity with a laptop, so for anyone hesitating even remotely I would suggest the upgrade.
So, specifically, I put a WD Scorpio Black 320GB 7200RPM drive and 4GB of G.SKILL DDR2 in my Penryn-based MacBook Pro. Following the directions posted at ExtremeTech, which were easy to follow, I slid in the new drive and RAM and then booted off of the Leopard DVD which allowed me to easily restore the entire machine from a Time Machine backup. I was actually quite impressed at that; I made a point of backing up right before I shut down the machine and then after about an hour of installing the drive, formatting it, and restoring from backup I had the exact same machine in front of me, only this time much faster. For reference, my XBench scores after the new drive and RAM installation are here.

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