Using the Window Mount is pretty straightforward, as anyone who has used a suction-cup device on their windshield for a GPS unit knows. After a couple of months of use, I have not had any problems with the suction cup not adhering to the windshield.

Newer promises that the Window Mount's flexible neck is "stiffer and more robust" than the competition. While I cannot vouch for the competition, as this is my first window mount, I can say the neck is indeed pretty stiff. Not so stiff that you can't move it, but stiff enough you have to put some effort into doing so. What this translates into is that once you've got the cradle positioned where you want it, you don't have to worry about it, and thus your iPhone, moving about while driving.
Once I had the Window Mount positioned where I wanted it, I popped my iPhone 3G into its cradle, plugged the iPhone into my Honda Pilot's power outlet, and off we went to the first hockey rink.

The Window Mount performed as advertised. Other than normal vibration you would get from an object so mounted in a moving vehicle, there was no travel of the cradle at all. (The stiff-yet-flexible neck at work.) I was able to tap on the iPhone as needed for navigation and iPod controls, with no movement of the cradle at all.

My only complaint about the Window Mount is that you cannot use it with your iPhone in any sort of sleeve or case, not even a relatively thin one like mine. It would be nice to see a future model with adjustable corners, so that one might be able to do so.

As it is, however, the Window Mount performs admirably, and over the two-plus months of usage, I have never been wary of my iPhone while it's been in the cradle. If you find yourself on the road quite a bit, and use your iPhone for just about everything, including navigation, the Window Mount is a must-have accessory.