IC's in high altitude and low temperatures
Devices 

The gravity at the top of Mt. Everest is only 0.434% weaker than at sea level - so no significant and not to worry about. The air pressure however is only about 1/3 of sea level. This could be a problem for some components that have air pockets such as DIP capacitors. The internal air will expand and could fracture the component depending on the design and build quality. I can't think of any SMD components that would would suffer from this, if someone can - please post a comment. 

Now the big problem is the cold. Most consumer made devices are not ready for low temperatures. LCDs contain crystals in them that could freeze and damage the components. The lubricant in the bearings for hard drives will thicken, slowing it down to the point that the device can't boot. Condensation could also be an issue as water droplets may form inside the unit and short something out. The thermal strain can also damage the board, solder joints or components. As the device cools and shrinks it the internal pressures on the parts could damage them if it was not designed for those conditions. In general the 0 - 45 C rating is not something the marketing department made up. 

Hard Drive that suffered from cold damage:



Source: http://vortex.accuweather.com/adc2004/pub/includes/columns/newsstory/2013/650x366_11062011_122191277.jpg

A BGA package that had a ball break after temperature cycling



Source: http://electronicdesign.com/boards/pcb-design-and-its-impact-device-reliability

ICS

Finally here is a paper on the effects of temperature on CMOS technologies. While the paper focuses on room and high temperatures the inverse is true for room and low temperatures. Propagation delays will be skewed and other timing issues will arise if the IC is no specifically designed to deal with that temperature:

http://ihome.ust.hk/~eekursun/papers/c25.pdf