Why do you find it irritating? What event in particular has caused you to conclude that the cooling is not up to scratch?
Your MacBook Pro is 91C - so what? Keep it off your lap and don't worry about the life of the thing. It'll be landfill in 10 years time.
I have no concerns about the lifespan of the machine; While I have little doubt that it would suffer catastrophic failure within 5 years were I to use it for that long, it will have been replaced and relegated to my parts drawer-after I disassemble it and fix as many of Apple's screw ups as I can, mainly to prove how stupidly easy it would've been to do it right in the first place-long before the AppleCare on it runs out.
The issue comes down to a philosophical difference between how I believe a computer should be built (or really, how I believe things should be done period) and how Steve Jobs, Michael Dell, et al. believe a computer should be built. I am a perfectionist. I expect things to be done to the highest possible practically achievable standard.
Apple, Dell, Alienware, HP, <insert every other mainstream computer manufacturer here> do not share that view. They exist, of course, to make money. And, given that they are businesses and generating income is, oddly enough, the primary purpose of most businesses, this is not really unexpected.
However, there are (as I see it at least) three ways of going about making money: Being cheaper than everyone else, being near-as-makes-no-difference the same as everyone else in terms of quality, features, and pricing (which will keep you afloat, if not necessarily hugely successful) or being distinctly better than everyone else and demanding a huge premium for your products. Apple sure as heck isn't the former, and they definitely aren't the latter (well, except for the cases where they go for the 'demanding a huge premium' bit).
It would have been, at the time the machine was being designed, a trivial exercise in terms of cost and additional development time to bring the MBP's CPU temperature under 100% load down into the mid 60*C range, if not lower, while keeping noise output under normal conditions similar to what it is now. It would have been a trivial exercise to engineer a cooling system for the iMac that would keep bsavitz's machine's hard drive within the maximum operating specifications set forth by the manufacturer of the drive,
which in all likelihood it is not (and I'd be happy to check that if he'd care to post the drive information from the system profiler), and again, doing it without a noise penalty to speak of.
It would have been laughably easy to keep the hard disks in my friend's G5 below 55*C (again, well out of the allowable range according to the drive manufacturer) at
idle, just as it would have to keep the CPU temperature nearer to 45*C than 65, without any significant increase in noise, considering that the PPC970 did not become a particularly power hungry processor until clock speeds were pushed past about 2.3GHz. I'd find you the IBM datasheet on the 970's power consumption if I could, but I can't track it down at the moment. This article:
http://arstechnica.com/articles/paedia/cpu/ppc970.ars which lists the 1.8GHz part as having a TDP of all of 42w (less than the current C2D desktop processors) will have to suffice. Air cooling a 42w heat load, while keeping the cooling system functionally inaudible AND keeping the CPU temperatures significantly lower than what I've seen from G5s is child's play for myself and many others; it would not have been challenging for Apple, either, had they had the desire to do so.
Ultimately, it comes down to this: They could do better. Much better. Without a great deal of expense or additional effort. All of them could. Not just Apple; just about every computer manufacturer save for some of the very small boutique companies could stand to improve in some way or another. And, by choice (read: because of the impact it could have on the bottom line, or on their development time, or whatever the excuse du jour is), they don't. They ship stuff that's "good enough" rather than "the best we can do". And while half(blank)ing it and calling it "good enough" might be, uh, good enough for you, I expect better.