I use it constantly on my iPhone, not so much on the iPad. Seems useless, I'd prolly use it more if the iPad had the weather and stocks apps. By the way, why didn't Apple include those and the clock app for iPad?
I think the major reason of this is that the iPhone didn't have any third party apps at launch. So Apple had to write some apps for it. When the iPad launched, it already has a few thousand native apps + hundreds of thousand of iPhone apps. So as a way to encourage users to download 3rd party apps from the App Store, Apple didn't include the stock, clock, weather and calculator, compass app for it.
Rarely on iPad. Usually just to check an email notification.
If it had the weather widget like iPhone I would use it more, but I have the Fahrenheit app on my home screen now so it is not such a big deal anymore.