The following easy-to-acquire info can really help to evaluate the quietness of a laptop IMHO. Contribute! See examples below.
1) Laptop mnfr & model number
2) Fan behavior (default start/stop temperature)
3) Support for speedfan, or other fan control software, and how it can improve the noise level.
4) Does the mnfr power management utility or bios help?
5) Subjective (or measured!) fan & harddrive noise levels & character
6) Can it run passive at low loads?
The holy grail would be a laptop that can stay below 60 degrees without help from the fan for light loads, yet still sport a powerful video card. I have yet to see the mobile GPU market really kick down the temps when their cards aren't doing 3D. They are seemingly a big liability still in laptops.
Also good would be a laptop that can idle at 50 degrees or less without active cooling. As long as it can stay under 60 though, it's a sensible choice for a low-noise laptop (all other things being equal).
The list! (i'll just keep editing this post as you guys post info)
NOTE: This is not a "recommended laptops" list. Everything goes here, the good, the bad, and hideously loud.
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Thin & Light
IBM X40 (12.1", Low-Voltage 1.4Ghz P-M, Intel Extreme graphics 2)
Seemingly quiet laptop. Fan spins up seldomly and is reasonably quiet. 1.8" Hard drive looks stellar noisewise. Speenfan doesn't seem to work. A+ battery life Gross overview only. Not yet tested in ideal quiet conditions. - cloneman
Dell Inspiron 2200 (1.3ghz CelM, Intel GMA900 768ram, 40gb)
Absolutely silent. Top of the laptop and palmrest never gets even warm, though the underside of the laptop does. Using I8kfangui, I've set it to switch the fan on low only when temps hit 60C. When placed on a desktop, temps never exceed 55C and usually hover around 50C. - davidstone28
Acer Travelmate 290e
Uses a Celeron-M 1.3GHz, and fan doesn't run until I do some intense computing. Hard drive is also very very quiet. No mods, no fanGUI,...
Palm rests stay cool. Bottom gets warm, and rear of keyboard, next to display. steve8pi
Mainstream
Dell Inspiron 6400 (15.4" Wide, Core 2 Duo 2.16Ghz 667FSB, Mobility Radeon X1400)
Fan control is supported by i8kfangui. With the fan off, temps will rise, even undervolted & idle. Cannot be comfortably cooled passively. Fan does not need to go higher than its first stepping under most use, (2400rpm), and its fairly quiet. The hard drive (120GB WD, reviewed on this site) is definitely audible, but not intrusive. A coil whine howeever seems to be present, and is piped through the sound card as well. It's dependant on load and speed/voltage control. This is my 3rd sample. A decent choice if yours doesn't whine. If the fan control would allow lower rpm it would be much better. 7/10- cloneman
Dell Inspiron 6400 (15.4" WS) Core 2 Duo, T5600 (1.83 GHz) with ATI Mobility Radeon X1400
@IDLE:
fan on/off at 48/38
With FanGUI set for 55/47, still cycles, but less often.
Passive: 63? degrees in cool room
Hard Drive I consider somewhat loud for home use, but not noticable in an office environment - steve8pi
Note by cloneman: My thoughts exactly. Not safe for passive cooling, but reasonable overall, though not close to SPCR standards.
Notebooks with Powerful Graphics
Toshiba a100-sk9 (15.4" wide, Core Duo 2Ghz, Geforce Go 7600)
No fan control support as of now. Fan is noisy, easily audible at 4-5m away. Fan turns on after a few minutes of use, and will never turn off after that. Laptop base feels cool on your lap, could definitely survive much higher temps. With better fan control this would be excellent. 6.5/10 - cloneman
Dell Inspiron 9400 (E1705) , T7400 CPU with Nvidia 7900GS Video
Uses 2 heatsinks and 2 fans to cool the CPU & GPU seperately. This results in a more efficient operation and the possiblity to cool almost completely passively on idle. Coil whine can be controlled & minimized, but is present. Impressive acoustics for a desktop replacement. Both fans are quieter than the 6400 model's fan, & the GPU fan is barely audible over the HD. This laptop overclocks very well (without affecting it's clocks in powersaving mode). Would have even better passive & oc capabilities if it has the dual heatpipe cooler for the VGA card (found in the xps version)8.7 /10 - cloneman
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