Others say...

"A Toy Fan"
I have had window fans that actually pulled out hot air from a second story room, allowing cooler first floor air to flow upstairs.

On the exhaust setting this window fan is more like a toy. When it didn't seem to be creating ANY air flow in the exhaust mode, I tested it by letting smoke drift about a foot from the fans. The fans didn't pull the smoke toward them, much less pull hot air from my 8x8 mini office. It might work best as a fan blowing IN, but I needed an exhaust fan. It is one of the more expensive small window fans and I expected it to be more functional.

"Functional, but missing some critical features"
This window fan is perfectly functional, but the absence of some features mars an otherwise desirable product.

Pros:
- It moves plenty of air, and keeps my 12'x15' room nice and cool.

- It has some nice automatic features, like a timer function and thermostat control.

Cons:

- Too deep to fit inside my window screen.
The back end of the unit is surprisingly large, so I removed my window screen. No big deal, right? Well...

- No dust screen.
After a few weeks of use, you'll start to notice dust and grime buildup along the path of the airflow. A decade or so ago, I owned a window fan with a removable dust screen that was easy to clean and prevented such buildup. Furthermore, due to the unit depth and lack of dust screen...

- The front and rear gratings are huge enough to let critters as large as bees in.
If your fan is not operating continuously, bugs will be able to fly into your house with ease. Either a dust screen or a closable vent would have solved this, but...

- No adjustable vent.
You can't direct the airflow, and you can't close the fan when it's not in use. But that said, even if you could close the fan itself...

- The adjustable length adapter does not sit flush with the rest of the unit.
This leaves a gap of approximately 3/8" between the window and the sliding adjuster. I taped the gap shut, but it's just another irritating design flaw.

- Annoying mechanical hum that's louder than the fan noise at low settings.
The hum appears to go away after an hour or so (either that or I adapt to it), but if the fan is using thermostat control, this noise will be prevalent whenever the fan is running. Speaking of the thermostat...

- The thermostat with digital readout is just silly.
Let's face it, the thermostat is built into the unit, approximately four inches from the path of airflow. If the temperature outside is 66 degrees, the temperature inside is 78 degrees, and your thermostat is set to 72 degrees, the fan will turn on, blow for about 15 seconds, 'read' a new indoor temperature of 71 degrees, and shut off, while the rest of the room is still warm. 45 seconds later, the air temperature will equilibrate and the fan will turn on again. While it's nice to be able to control the indoor temperature, the digital readout is inaccurate and unncessary.

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I'll probably keep this fan around for the rest of the summer, and maybe cut a piece of foam or tape an air filter onto the fan intake as a temporary solution, but bottom line? I'll probably hawk this fan to some poor sucker on the first hot day next summer at a yard sale and buy a better unit.

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Update September 1, 2008:

Okay, so this thing spews bugs into the house even when the fan is running. Heck, the fan may even be amplifying the problem by actively sucking them in! Anyway, I grabbed an old window screen, cut out the mesh, and hot glued it to the outside of the fan, and it seems to be keeping the bugs out, now.

"Great Window Fan "
I have two of these and they are the best window fans I have used. They are quiet compared to the other window fans I have and you can set the temperature and speed you like and forget about them. There are 3 variable speeds and two modes intake/exhaust. The only time I use the A/C is when the humidity inside the house gets high, otherwise this fan does the trick.

"eh..."
Not so much. Got this fan a couple years ago - my NYC apartment has remarkably poor airflow for a place with more than an average amount of windows - and I was hoping that this fan would create a little more. It ebbs, here and there, but if that amount of wind were to be blowing through an open window, at, say, a lake house or somewhere else people wish they could afford to go to feel generally refreshed, I'd probably try to find a better window. On a well made wind-chime, you might get two dings out of six.

My goal of airflow was reduced to that of containment - since it was in the kitchen I figured that at least, when I cooked in warmer weather, I could exhaust just enough hot air to prevent it from spilling into the dining room where the AC was struggling to reach as it was.

That goal, not quite being reached either, was reduced to running on intake during the winter whenever I had the oven cranked up. This goal was definitely met. It was almost as if I had... opened a window.

This fan is what I would call remarkably quiet. Granted, it's in the kitchen, where I don't sit to relax anyway, but it is sufficiently un-noisy that I feel it's worth... well... remarking on. If you have a house in the country and want a nice, small amount of airflow while you're sleeping at night, you'll still even hear the crickets over this one on its lower settings. Maybe if I had a nice country house with crickets outside and everything, I would have given it a higher rating.

I'm waiting on the Honeywell HW-628 Twin Window Fan , for which the vast majority of reviewers (145 of 167) have given 4 to 5 stars. I like stars. Stars are good.

One final, slightly less rambling note: fellow city dwellers, who are familiar with that special black matter (pollution, or what have you) that accumulates around windows, etc.: if you want a window fan that you can clean without rubber gloves, two old toothbrushes, and a can-and-a-half of Goo Gone, and you don't have a serious obsessive/compulsive problem like I do, don't even CONSIDER this fan.

"The Longest Lasting Fan"
We bought this fan over 2 years ago when we first moved into our two story home. We needed a fan for upstairs to help blow in fresh air in the cooler months and suck out the hot air in the warmer months. It did just that! We had continuously used this fan for 2 years straight...day and night (only turning off once in a while for inclement weather) before the fan died! You can beat it lasting 2 straight years of continual use...day after day!
The fans are great when you are painting a room in your house, or doing other repairs that require ventilation. They help to suck out the dust, paint fumes, or funky odors. They are easy to store (We have the dead one tucked away in case we can figure out how to repair it.).
We found they did best upstairs, where we have no central air, to suck out the hot air all day. By the time you go to bed, one fan on one end of house, has sucked out the hot air and brought in the cool air at night...making it virtually unneeded to have a window unit.
I was so sad when it died. I bought 2 similar style fans...but you have to manually take the fans out and turn them around to use the exhaust feature. That is a real pain. I am so glad to have found these fans again. I can't wait to order more!