My last two houses had whole house fans and they were great.
My current house does not, but I don't miss it too much, but I'd still like to have one if I could (I haven't been inspired enough to install one yet).
Like others have said, the whole house fan works well when it is cool at night and warm during the day. In spring and fall here in Virginia it's great.
House fans are also great for evacuating all the smoke from the kitchen if something gets burnt. They are also great if you leave the house for periods of time and want to freshen it up quick!
Where it's not so great is during the summer where temps are high and humidity is through the roof. I was just sitting here in the comfort of the ice cold AC thinking my wife (and I) would kill me if I turned on a house fan. All the cool low humidity air would get sucked right out.
What my house would benefit the most from right now (with the AC on) would be a gable vent fan of some sort, just to move hot attic air out faster.
The final thing is humidity, included is a pic of a mountaintop house nearby that I looked at some time ago. It has no central air, but several house fans. The only problem is that pulling in all the moist air (humid, or damp mountain air) reeked havoc on the interior, especially drywall. Cool house though!
