The wet sheet idea would work well in dry areas, that's about it. Personally, I'm a big fan of putting white poster board or cardboard in south and west facing windows, at least during daylight hours.

Uh, yeah ... here in muggy Virginia the idea of opening your windows after dark and hanging a wet sheet in the window is a non-starter. When you consider that we had to buy a dehumidifier for our basement (and we don't have any leaks in it) because the humidity down there where it's cooler is routinely above 60% ... Well, let's just say that it doesn't matter where you are in the Commonwealth, it's muggy from about January (when it's a damp cold) through December (when it's back to being a damp cold). A "dry" air day around these parts is very rare.

Another thing ... do NOT turn your a/c OFF while you're at work during really hot periods. This is about as smart as turning your HEAT off during the winter while you're at work. It will take more energy to cool off your house or apartment when you get home (and who enjoys coming out of 90+ degree weather into a house where it's 95+?). The smarter thing to do is turn the thermostat to a higher temp and put it on "energy saver" which ALL a/c units have these days. That way you can turn the temp down when you get home and it will take less time and cost less energy to make it comfy in your home.

Cat,

I have to agree, turning off the AC when it is hot just because you're not there is pretty stupid. Changing the temperature higher is a good way to save some energy, but with the exception of desert areas, the humidity rise if you shut it off, will just take that much longer to overcome. Too much up and down temperature variation is also a really good way to promote condensation and mold growth too. If all you have is a smallish window unit, you definitely don't want to shut it off during the hottest part of the day.

And as to the wet sheet idea at night, the air is almost always more humid at night. They use evaporative cooler in dry climates and they work pretty well up to around 40-50% humidity, but they are best when it's down in the 20-30% range. I use one in a barn and it feels pretty good when it's blowing on you, but it will raise the humidity somewhat so there's a trade off. At about 25% humidity, a twenty degree temperature drop isn't uncommon. Actually just a fan blowing on you feels pretty good unless it is extremely hot. The fan helps improve your own human cooling system helping evaporate moisture off of your body. A fan will constantly blow slightly drier air across your skin allow your own evaporation to be more efficient. A simple box fan is cheap and they take very little energy to run.

When it's really hot, sometimes a quick shower with just a mild towel drying to where you are just damp and then a little fan time will cool you down a great deal. A soak in a luke warm tub does a good job too and it's pretty relaxing. Shedding excess clothing and exposing more skin surface works too in a non air conditioned home or one that has undersized AC. If you can take the humidity down a bit, even 80 degree air can feel pretty comfortable if you are minimally dressed. It is often said that it's not the heat but it's the humidity. There's a lot to that. The reason AC works as well as it does is because it takes the humidity out of the air. Humidity has a big impact on how hot it feels.

A good energy idea when it's hot is to make that move to switching from incandescent lighting to compact fluorescent. Not only do these save money on energy costs, but the generate far less heat. A 100 watt incandescent bulb is adding about 300 BTUs of heat every hour that they are on. If you have about 5 of these bulbs lit in your house, you might as well have a standard small space heater running on its highest setting. CFLs will use only about 25% or less energy than the equivelant incandescent for the same amount of light. They generate far less heat too.

There's a lot smarter thiings to do to stay cool than the suggestions given here.