I upgraded my MacBook 1.1 (yes first gen!) Intel Core Duo with Toshiba 5400rpm 60GB HDD to a Seagate 7200.4 7200rpm 320GB ST9320423AS HDD. The performance jump is outstanding. My MacBook from cold gets to the login screen in less than 30 seconds. After logging in the MacBook would be pretty much unusable for about 20 secs on the old Toshiba drive because of programs that load on login. With the 7200rpm drive these just 'pop' onto the menu bar. I couldn't stand Cover Flow on the 5400rpm HDD the previews took so long to load but on the 7200rpm the previews load in a snap, just make sure you turn off file sizes column in cover flow mode though. Garageband the 5400rpm struggled with 3-4 tracks, the 7200rpm easily handled 8 tracks (didn't bother testing more tracks as that's the most I would ever need). I haven't seen any loss in battery life with the 7200rpm drive and it can be powered with a single USB socket in an external caddy which backs up its lower power specs. I've compared my MacBook with my Aluminum iMac 2.4 GHz Core 2 Duo with 3.5" SATA II HDD and honestly the MacBook with this 7200rpm drive is just as fast apart from processor intensive tasks like h264 encoding. A 7200rpm HDD is a terrific upgrade, imho far more noticeable than doubling memory. Processor speed wouldn't make a difference for 95% of daily use, the Intel Core Duo handles pretty much everything I need it for including 720P HD viewing, heck an Intel Atom can do nearly everything the non-pro needs. p.s. I also connect an external 19" LCD to my MacBook, Mac OS X really handles multiple screens well and 19" LCDs are really cheap nowadays so well worth doing.