sorry (actually not, Launchpad's fault, not mine): reposting the comment with corrections, as this fucking pathetic bug tracker doesn't let me edit it
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I suspect there are actually two (or more) issues here.

1) Thermald issues:

1a) As described in the original report, various types of CPU clamping kick in before the fan has an opportunity to do its job alone

1b) Plus, as described in comments 20-23, CPU clamping not stopping after the temperature has gone back to normal.

2) BUT THERE'S SOMETHING ELSE, which seems to be outside thermald, and I wonder if it actually explains issue 1a on its own (but of course not 1b):

Something (in software), even without thermald running, seems to prevent the fan from spinning as fast as needed.

What I base this theory on is:

- I now always stop thermald as soon as I turn my laptop on.

- when I do stuff that consumes a lot of CPU (like watching video -LOL- I know, it shouldn't consume a significant amont of CPU, but apparently there are other bugs), the temperature grows and grows.

* Now before you say it, YES, my fan needs some cleaning. That's not the point.
* If my fan alone was the problem, the temperature would go up as it does AND
* the fan would spin at its maximum speed, as already "proven" in my previous comment.

I don't know how to see the actual temperature, but I know that it goes high (i) by touching the bottom of the laptop and burning myself, and (ii) because it gets to a point (remember: thermald is off) where everything becomes incredibly slow. When it is, top shows that all the CPU power is being used (while doing the same amount of work that was not saturating the CPU before) - now that could be either because some software bug causes more and more CPU power to be used, OR because the total CPU power is less because some extreme (probably hardware) protection mechanism is lowering CPU power to stop it from burning. The confirmation that it's the latter, is that trivial processes doing virtually zero work seem to consume a high percentage of CPU.

Now, all this would be expected and could be attributed to a dirty fan, IF at this point the fan was spinning at its maximum speed. Because, if the span is being incapable of coping with the temperature growth, by definition it should be working at its maximum, that being insufficient.

And the fact is that that is not the case: I get to the above described situation while the fan is WAY below its maximum speed.
Remember: all this with thermald off.

The FINAL PROOF that something is preventing the fan from going as fast as it should is that:
- if I turn the computer off and on, the fan spins superfast while the boot menu is shown. That means that, when the OS with all its parafernalia is not yet running, the hardware somehow "knows" that it needs the fan to spin a lot faster to cool it down. Then, as the system boots, you can hear the fan go to the minimum (or close), and then speed up again, but much much less.

Also by suspending I can reproduce a similar effect, to a lesser extent:
when I suspend and resume, the fan goes quite a bit faster than it was prior to suspending, but not quite as fast as when rebooting. Then it gradually but noticeably slows down. It may be expected that it slows down, if it was managing to quickly reduce the temperature, but it is quite clear that it slows down much faster than the temperature goes down. The proof of this last statement is that (i) if I now reboot it will go much faster; (ii) it's obvious that the temperature cannot be going down so fast, and (iii) if I keep doing the same cpu-heavy stuff I was doing, in a matter of seconds the system is slow again (meaning, as described above, that it's so hot it has to reduce CPU performance in whatever way it does it) but the fan speed doesn't go up; indeed it keeps slowing down.

So, my conclusion is that whether or not thermald is running, SOMETHING PREVENTS THE FAN FROM GOING AS FAST AS IT SHOULD.

Note that whether or not the fan is able to do its work at its best, or even sufficiently (i.e. it's dirty) is irrelevant. Whether or not that is the case, if the temperature is increasing, then the fan should be going faster. Which means that if it is not capable of keeping the temperature within the established limits, it should reach its maximum speed.