Hi Paul Bailey,
I just bought Coolbook for my 15' Macbook Pro Unibody (2.4ghz) yesterday. I recently asked your very question about Coolbook and warranty / AppleCare and the response I received from iVmichael was that it would be fine (thread visible here:
http://discussions.apple.com/thread.jspa?messageID=10132068� ). I read the Coolbook instructions yesterday and it said that Coolbook couldn't damage your processor. I did some experimenting with it and even putting the highest speed at the lowest voltage it would let me use on Coolbook only resulted in a kernel panic which just told me to turn the computer off, which I did. When I turned it back on, there were no problems at all so I don't think you'll run into problems with Coolbook or at the very least, that's been my experience.
I played around with the voltages a bit however I found that for most things I do, it didn't make a noticeable difference. I mostly just use my Macbook Pro for web browsing and email, which are already very well handled at cool temperatures by Apple.
I think the one thing to keep in mind is that even if by lowering the processor speed you're able to use less power through undervolting, you'll then end up with the processor working more time (eg. 2.4ghz processor will finish an encoding job much faster than a 1.8ghz processor) and that higher speed processor might actually end up being a better fit because once it finishes the demanding tasks, it'll underclock itself while the slower Coolbook-enabled processor is still working at most likely a higher frequency + voltage.
From what I've read, everyone's Macbook Pro will have different results with Coolbook, as some of the Intel chips are willing to run (and be stable) at lower voltages than others, so some people will get more (or less) benefit than I experienced. I was able to get mine to run at 2.4ghz while using 1.0625 volts instead of the default of 1.1375 volts, so my CPU is running about 7% more power efficiently now. I had similar power efficiency improvements experimenting with different speed/voltage combinations. One thing to watch when lowering voltages is that some people have experienced a Core getting disabled (because not enough power is flowing to keep both enabled). If lowering the voltage causes this, you might find your Macbook Pro getting hotter instead of cooler, especially if doing anything that on one CPU causes it to constantly work at it's maximum performance.
I'm not sure how much of a difference +7% CPU power efficiency would make in battery life, however mine seems to run about 2-3 degrees Celsius cooler which is nice, although it wasn't bothering me at the higher temperature. What I've heard mentioned in other threads on the Apple Discussion forums is that a cooler running Macbook Pro's battery should be able to go through more charging cycles than a warmer running one because of the effect heat has on the duration of a battery's life, so that's another definite plus.
For battery life, you should get a pretty good extension (better than Coolbook) by lowering the Macbook Pro's LCD/LED brightness to the minimum or as low as you can tolerate if you aren't doing that already. I've heard that even not having the keys backlit when on battery power can add about 45 minutes to battery life as well. For the $10 Coolbook costs, it's worth it in my opinion.
As for experimenting with fan speed, I definitely think it's a bad idea to have the fan running at max speed or ramping it up substantially over the default Apple settings. Like you said, it'll make the fan age faster and I've heard replacement fans aren't all that cheap (especially when you factor in labor). I really wouldn't know the answer to this, so I'm just speculating, however I personally would see fan failure resultant from smcfancontrol (or another fan speed program) as the Macbook Pro owner's fault and clearly not the fault of Apple if the fan were to fail because it's being used for extended periods of time at substantially higher speeds than it was intended to run at. I've seen some people say it wouldn't affect the warranty, however I think it's best that you contact AppleCare directly and ask just to be safe if this is something you're considering doing -- I haven't managed to come across an official answer from Apple.
What I think is a good idea would be to increase the minimum fan speed a bit. My Macbook Pro fans usually run at around 2000rpm, so by increasing the fan speed to 2200rpm, I make it run a bit cooler while presumably not doing much to shorten fan lifespan. I may perhaps even be increasing fan lifespan as it now takes longer before the fans need to run at a higher rpm because they're doing a better job at keeping the Macbook Pro running within it's designed thermal envelope.
