I bit the bullet today and purchased CoolBook. It's been activated but I haven't rebooted yet cause I'm still doing work. I'll update this post when I have some results. EDIT1: Finally got it installed after a few hiccups. After first initial reboot, OS X said it didn't load properly for some reason. I tried loading manually with kextload, said something about permissions or ownership. Reinstall + reboot fixed that. TAKE THESE RESULTS WITH A GRAIN OF SALT. This is my first review of anything, ever. And I probably suck at benchmarking/testing, so there. Some info: I have a Macbook Pro Core 2 Duo 15", only upgrade is the extra 1gb stick of RAM. I use Fan Control, Base Speed is 2000 RPM, Lower threshold: 50C, Upper: 80C. Usual idle temp is 55C. Ambient temperature is 29.5C at the moment. I use MenuTemperature to monitor CPU temperature. At full CPU normally, fans ramp up to 6000 RPM and then temperature stays average at 73C after initial spiking up to 82C. I realise I should have tested my MBP more thoroughly earlier but I didn't bother. Test 1: Clock speed set to 1002mhz (1.0ghz) and voltage to 0.95v. Then I had two instances of 'yes > /dev/null' running, and the temp rose slowly to 60C, when the fans kicked in slightly, and now it's hovering at 58C. Verdict: Undervolting and underclocking most certainly worked, with fans not breaking 3500 RPM and temp still not breaking 60C. Test 2: (IN PROGRESS) Attempt to find ideal lowest voltage for highest frequency and see how it fares. Started off with 2.16ghz/1.1v. When maxed out, temperature hit 67C, with fans hovering at 4400 RPM. A definite improvement already with a 6C temperature drop and 1600 less RPM for the fans. Second try was 2.16ghz/1.05v. At max, temp was 65C, fans hovering at 4170 RPM. Another 2C off. 2.16ghz/1.00v: When putting load on the CPU, around three seconds later it crashed and rebooted. 2.16/1.025v: Temperature hit 65C, fan RPM hovering at 4150. Not much of a change, really. 2.16/1.0125v: Temp is 63C, RPM 4050. Slight drop, but then crashed after I hit 'Save' on this post. I'd probably stay at 1.025v for stability. Verdict: Works quite well at dropping your temperature and fan speed. Test 3: (HALF COMPLETE) Test battery life with 1.0Ghz/0.95v. Brightness on 1 bar, wireless, bluetooth off, connected to the internet, Firefox, Adium, iTerm, MiniBatteryLogger on and it's giving me around 3:30 at the moment. I don't have time to time it exactly how long it takes to die, so it'll have to wait. Test 4: (NOT COMPLETE) Test battery life with 2.16Ghz/XXXv. Test 5: XBenches. 1.0ghz/0.95v: 64.04 2.16ghz/1.1v: 108.00 More to be added later. Comments/suggestions/ideas for more tests?