Cold

It's 19 degrees here in Portland. You made me curious as to how cold my studio was getting - the oil filled baseboard heaters I installed are off. It was 63 degrees down there, not too bad. I tapped into my HVAC when I built it just to circulate the air and added special sound trapping, it was elaborate and works great from an audio perspective, but ended up a bit anemic from an airflow perspective. That's what you get when you are a hardware/software/systems engineer that thinks he knows it all ... LOL! I tried. That aside, it is keeping up for now.

 
      The condensation angle is a good one. Your computer will probably like the cold as long as the temp is not low enough to affect the lubricants in the fans (well below 35 I am sure).        
 
      Dan

I hadn't thought about humidity. I actually have a hygrometer on the wall, although I almost never look at it. If I can trust it, it's telling me the humidity's rather low. That's probably right, since it's pretty dry outside, too.
 
My biggest concern was for microphones and speakers, which represent my biggest monetary investment. The microphones are in pouches, inside a metal briefcase with dessicant (I save those little silica gel packets that come in aspirin bottles and such, and throw them into the mic case.) The microphones are probably OK.
 
Speakers, I'm not sure about. I'm trying to think of a reason why they'd care about temperature. My main speakers are made of high-tech materials that can stop bullets and the tweeters are plastic, but my less-expensive subwoofer has a coated paper cone. Both have a surround made from a flexible rubber-like material attaching the cone to the frame, and I wonder if it might lose elasticity in extreme cold, and then possibly crack or malform in use.

I do remember that after reading an article about doing outdoor sound in SOS?  I have always sprayed my paper cones with Scotch Guard. Front and back. Note, I have not done this to my NMS10's. But All others were treated including my Bass and Guitar amps.
 
Anyhow I think electric compenents have a wide range of temperature tolerance, There would be a point where stuff might crack if to cold. I would think mikes in pouches are OK, at least SM 58 / 57 types would be.

When I lived up north (for many years) and transported my equipment to a job in a car trunk, in the winter it would be very cold by the time I got to the job.  Especially my Pedal steel guitar which has lots of metal/mechanical parts.  Same way with an amp and effects.  After unloading, I would wait til they got back up to or near room temperature before turning on electronic gear or trying to tune up the steel. 
 
I don't have a studio that is in an unheated area, but if I did I would turn on the heat and let the room get up to temperature before turning on equipment.
 
Here in Florida, with the high humidity in the summer, that is a concern in non-air conditioned locations.  
 
I used to work as an amp tech in Nashville.  I've never had any amps that were in for repair that potentially were affected by being in the cold.  Back in the early 70's when I was there, unheated trailers were common for bands and apparently it had no affect on the equipment.  Obviously, if an amp had been stored for an extended period in a shed somewhere that is a different story. 

Dave I did a bit of digging around for you. Here to begin with is a SOS article which brings up a few points:
 
http://www.soundonsound.com/sos/mar10/articles/qanda0310_4.htm
 
I looked up some specs for the following items and they indicated some temperature ranges:
 
Quest speaker  -10 C to +55C Other speakers though specified operating ranges as low as -25C and -35C in some cases.
 
Shure PG57 Mic -29 C to +57 C
 
Soundcraft Mixer +5 C to +40 C
 
Korg Kronos synthesiser +5 to +35C
 
Notice the mixer and the Korg Kronos did not like going down too far. The Korg synth obviously does not like getting too hot either +35 is easily obtainable on a pretty hot day. That would run pretty hot inside I would imagine under those conditions. In the manual also the Korg synth is very clear if there is condensation it also should not be used. Speakers and Mics seem to be OK although the Quest speaker is borderline in your case. (Other speakers went well below that though) These are operating and I guess storage temps too. The point that Mike mentions is important but also I have never felt great about all the soldering inside a lot of gear being kept at super cold temps. (and then coming into hot venues and going back out into cold temps again for longish periods) I lived in Canberra (Australia) for a long time and the temps there in the winter go down to 0 C and under. After doing gigs and getting home late I often brought the electronics gear inside. Left my drums out there though! Mechanical things like tape machines definitely don't like the cold.
 
Personally I don't think it is great for anything but that could just be me being paranoid.

Quest does make speaker systems for outdoor use.

Bonzos Ghost
Going from very cold to hot (if you have hardware that runs hot when on) can cause solder joints to fail. Not that common of a problem but it can happen. I've had to re-solder the odd power supply capacitor twice now in one of my ASR-10 samplers - which runs very hot. Quite a job taking it apart so I could get at them, but not that hard to do really. I'm not an electronics guy by any stretch, but I can solder OK as I've made a lot of cables over the years.

I've seen that. Having worked at an electronics mfr - seen lots of tests of devices being shock heated and cooled (mostly industrial mobile devices). Best to let your avg electronic things acclimate for a couple hours before use.

Yup, you learn that trick when you tour Canada, Alaska and the northern tier states. Guitars stay wrapped until they've had time to warm up. Applies to groupies, too.

as I have an interest in old 8 bit computers.. a lot use old paper disc caps etc. that *DO* need replacing as they age and you will get a stink and a pop when they eventually do go.. extreme temps e.g. lofts / basements do them no favours.... same goes with vintage electronic stuff that needs re-capping.. and some stuff is probably well known for the PSU going pop because of not being used in 10-30 years.