I think it will be as popular as the iPad. It's small like the iPad, but it will be faster and it supports flash. Not to mention it has a USB port along with some other things the iPad is missing. If the iPad had all these features the iPad would be in more peoples hands.
I like both and may end up owning both, but this is simply wrong. Apple is selling iPads faster than it can make them, ther is simply no way it would be "in more peoples hands". Now that the supply has ramped up, it will be in Best Buy, Target, etc, and will be in a LOT more hands.
Anyway, the iPad still has many advantages
MUCH longer battery life. Andy Ihnatko just used a new Air for 5 hours of normal use and 2-3 hours of heavy use, not even half of what an iPad can get.
No 3G option, an iPad can access the Internet from anywhere.
Much easier to use OS.
Touch interface.
Much cheaper software AND a greater variety. all sorts of specialized apps which aren't on OS X/Windows/Linux. If you own iPhone apps, you can use them without buying therm again.
An intelligent virtual keyboard. If you are entereing a web address, there is no space bar (impossible character), but you can enter .COM with one keystroke,
The Air has some advantages as well, for those who have wanted an Apple netbook (myself included) it will be a good solution. I would have preferred a faster processor but at least you can special order 4GB of RAM.