I do undervolt my CPU, which is AMD Athlon X2 QL-64 from 1.1V (IIRC) to 1.05V and in power saving mode is 1.05GHz 0.9V. Less heat even when gaming, more battery life when using battery. My opinion? I recommend it to everyone, its not dangerous, and its a lot of benefits like you said. The BSOD is because you don't do any reading before doing it, each CPU have its own limit on how low you could go

I use k10stat to undervolt my CPU, I don't know how on Intel side though

Nah, most CPU have higher voltage that they ever used. Like us, most of us eat more than we ever need, that is why the obesity increased nowadays

On AMD system (at least on my laptop) it never goes to full speed when running on batteries even when playing games unless I forced it in k10stat, maybe it have something to do with Windows Power Options

Following the format:

LYN ID: Najmods
Notebook/Laptop Model: ASUS K40AB
Processor Model: AMD Athlon 64 X2 QL-64 2.1GHz 512kB L2 cache
Stable Undervolted Voltage:
DID: 0 FID: 13 Voltage 1.05V CPU frequency 2100MHz
DID: 1 FID: 13 Voltage 0.9V CPU frequency 1050MHz

Yes without backpanel you could achieve insanely low temperature, I even managed to get 38C CPU and 44C GPU temperature in non air conditioned room. It could get dusty but don't worry unless you could used it on dusty environment. Using notebook cooler minimises it

You could use multiple temperature monitoring software like HWMonitor if you think the temperature is inaccurate. But don't worry, most laptop CPU are designed to handle high temperature, 90C+ is common, some even playing games at over 100C but its rock stable. What other things could be the culprit? Maybe dust if your system is few months old, but ultimately laptop is hotter than desktop because small heatsink and fan to cool them down

Is it so hard to Google for it? Sitting around and worried won't get you anywhere. Read this.

AFAIK all the new Athlon/Turion CPU are supported in k10stats.