Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
There'd hardly be a difference, based on my experience with replacing 5600rpm drives with 7200rpm ones in several laptops.

Once a drive is spinning, it doesn't take much power to keep it that way.

A 7200rpm drive will do its job in less time, as well, potentially letting it sleep earlier in some applications.

But I really doubt you'd notice much difference. Speed and responsiveness might be another story, however. You will definitely notice that. (But the improvement from jamming in more RAM is even more noticeable.)

Note that the lower spin-rate drives have larger storage capacity. This is because larger tolerances must be used for track spacing in the higher-rpm drives. I'd rank the higher-rpm drives as slightly more robust physically, as a consequence.
 
(But the improvement from jamming in more RAM is even more noticeable.)

Totally disagree with this assessment - unless you're running virtual machines and such, 4GB is plenty for most people. The 7200rpm drive is just enough to get rid of a ton of beachballing and waiting around when you launch programs... while its not an SSD, it brings wait times down to much more tolerable levels for most everyday tasks.
 
I agree that it's worth it. I would not pay Apple the $100 for the upgrade though. Instead I'd go over to newegg and get a nice 500 GB 7200 rpm Hitachi or something and an external case (for <$100 total) to house the slower 5400 drive in as a TimeMachine backup.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.