Asus Q-Fan control - to enable or not?

[dta]

Many motherboards feature some form of fan-speed control, eg. Asus Q-Fan control (BIOS or via utility). Gigabyte and MSI motherboards also have has that feature (named differently).
 
Some are also controllable via SpeedFan (or similar utility).
 
 
Just wondering, what setting do you usually use for your CPU fans -- do you have this "Smart Fan" control enabled?  (Asus Q-Fan can be set to Optimal / Silent / Performance, depending on which revision of Q-Fan).
 
With lower fan CPU fan speed, the CPU stays a bit warmer than when the CPU fan is always at full fan speed.
 
Also, does having the fan @ full fan speed shorten the life of the fan (but can possibly slightly prolong the life of the CPU since it stays a bit cooler).
 
This is using the stock Intel CPU cooler. Let's say  if the normal usage environment is generally pretty light (eg. MS Office like tasks, and not CPU-intensive nor gaming tasks).
 
What if different usage environment, what would you generally use? (enable the Q-Fan control or leave it disabled)?
 
 
Q-Fan (or other "Smart-Fan control") disabled:
+ good for CPU: fan @ 100% fan speed, CPU temperature possibly slightly lower, and thus can possibly prolong CPU life
- not so good for casing: more dust gets sucked in since fan is always at 100% fan speed  (not in an enclosed/aircon room)
- not so good for fan: fan life may be shortened since it's always running at full speed, also more dust may attach to the fan assembly, which can also affect the fan mechanism if not regularly cleaned
 
Q-Fan (or other "Smart-Fan control") enabled:
+ good for fan: fan's life may be prolonged since it's not always working at 100% speed
+ good for casing: the casing may be slightly less dusty since the fan is spinning weaker and sucks in less dust particles
- not so good for CPU: CPU stays at a slightly higher temperature

[bravoexo]

I only need the fan speed reading for the pumps on my system.  Otherwise I control all the fans I have with a fan bus controller up front.

[juke]

I use 100% power all the time. But if I'd control them, I'll use a hardware fan controller. It's safer to know that your fans are properly controlled than your fan app crashing and your fan runs on its own, or not run at all.

[bravoexo]

I did watch JJ of Asus demonstrate those new fan control w/ their Z77V's mobo...quite interesting.  Full PWM all headers sila.  Gigabyte only has two ata that are full PWM...

[juke]

^What's the amperage of the fans attached?