I took on the tech equivalent of abdominal surgery... one wrong move and you're laptop is crap. I had a huge success with some helpful tips.
After waiting a week to get the main logic board replaced under the AppleCare warranty, I booted my MacBookPro to discover that the Apple techs had nuked my user account, deleting all my personal files.  The concierge at the store couldn't explain why this happened.

I soon realized this was a good time for an upgrade. I had been bumping up against the 120 GB limit of the OEM drive for too long.  A quick drive over to Tiger Direct in Durham and I bought a new Seagate Momentus. A 7400RPM, 500GB replacement drive for $120.

Before finalizing my purchase I did a bit of googling on the iPhone to determine if this would be a good fit for the Mac.  Issues like heat, noise and performance were the main criteria.

I got tremendous reassurance from Ian Garris, a writer for TechWareLabs. Not only was this new drive bigger and faster, but it also uses 25% less electricity than my old drive.   How often do you get bigger, faster and more efficient at the same time?

Disassembling and reassembling a newly rebuilt, in warranty MBP took some cojones, even if I do say so.

There are great step-by-step directions at Extreme Tech Upgrade Your MacBook Pro's Hard Drive.