I just swapped out the stock 80GB hard drive on my Macbook with a 250GB, 7200rpm model that I picked up from Newegg. The process was not all that smooth, and I didn’t get a ton of help from the internet, so I thought I’d try to earn a little bit of karma and put some observations here for Google to index:

• There are good tutorials on this process to be found; here is the one that I used.
• The EMI (electromagnetic interference) shield on the hard drive (which the just-mentioned tutorial calls the “bracket”) is a royal pain in the ass. The screws are Torx T8. As I am not a computer repair professional, I don’t keep every fricking screwdriver under the sun in my apartment. The screw holes in the shield are big enough that you can slide them over the head of the screws, and I thought to myself “Hey, why bother even taking the screws out? This thing can do its EMI-shielding without being attached!”
• This was a mistake.
• I slid the new hard drive into the bay with the EMI shield resting on top. Disk Utility did not recognize the hard drive. Since the shield was not attached to the HDD with screws, I couldn’t use the ribbon on the shield to pull the thing out. After about 20 minutes of messing around with some sticky tape and gravity, I managed to get the new, screwless HDD back out the of the computer.
• It turns out that the reason that the drive wasn’t being recognized was related to the screws: they not only hold the shield on, but they act as guides to make sure that the disk’s connectors line up right. I managed to get one screw out of the old drive with a flathead screwdriver and another one with an Allen wrench. The other two were screwed way too tight to remove without the right tool. I put the two screws I had removed into the connector-end of the HDD, since that’s where the alignment really mattered. That did the trick – Disk Utility saw the drive.
• As for data movement: I tried the Restore from Time Machine Backup feature on the OS X installation disks. It took about two hours, told me that it had been successful, and then failed to boot. The Leopard install program recognized that there was an instance of OS X on the drive, but I couldn’t boot into it (might have something to do with the fact that the old disk image had driver data associated with a different kind of HDD, I guess).
• So I wiped the new disk clean and tried installing Leopard first and then using Migration Assistant to bring over my things. After running for about an hour and a half, MA got hung up with “Less than a minute remaining” for about an hour. A little Googling told me that this is fairly common (and might have something to do with printer drivers?). I shut down the computer (by holding down the power key until it shut off – the only way to get out of the MA) and rebooted, running through the OS X setup program again, except this time not importing any info.
• The setup program created a new user account for me, but the old one, with nearly all my settings intact (minus the ones that were dependent on Leopard updates that weren’t included on the DVD), was still there.

All in all, replacing the hard drive was probably one of the most bitchin and gnarly experiences of my life. Good luck.