A lot of users are worried about fan speed changing. I agree with them, but not completely.
Like every other operation involving a PC and its hardware, not everybody should do it. I mean: even if I've got some knowledge about my car, I do not spend my time hacking it :-)

Anyway: changing fan speeds can't be considered that harmful, because every hardware manufacturer should have taken into account the chance that a fan will ever fail and most of us have got a PC with a fan that's no longer running since a long time.

Personally, I'm much more afraid of those heatsinks that require Hulk to set them up, and when you're done you hardly realize that all that force is held by a couple of really small plastic pieces that might easily break. What would happen then?

Have you ever considered the weight of a performance heatsink? Have you ever considered what happens if you move your PC for a lan party? A friend of mine broke his CPU transporting his PC this way.

One final note goes to those temperature sensors built into recent CPUs. Well... if you search the web you'll find a really interesting movie where a PIII, an Athlon and a P4 are filmed while the heatsink is removed: the PIII simply hangs, the Athlon lovely burns with the motherboard itself and the P4 simply slows down working perfectly and resuming normal clock speed when the heatsink is restored in place.

A second issue is about the chance that a fan will break after having been speed changed.
Well... that might happen, but, according to my experience, the chance is very low (0% for me :-)).

If it was that likely to happen (that a fan could break), why did almost every hardware monitoring chip manufacturer add that option? And why did motherboard manufacturers include the circuitry to support it? :-)