It definitely fills the gap between ipod and netbook and netbook and laptop.
I see it almost like ipod - ipad - netbook - ipad - laptop. (if that makes sense). The netbook is going to do some things the iPad isn't and the iPad is going to do somethings the netbook isn't.
The question is does that gap need to be filled...
My iPod certainly has it's place in my digital lifestyle. My laptop certainly has a place in my digital lifestyle. My netbook certainly has a place in my digital lifestyle. I'm stating to see how the iPad could fit in on both sides of the netbook - using what your wife said, I would bring my iPod to the gym but I can't read an eBook on it. I could read the eBook on my Netbook but I wouldn't bring it to the gym. I bring my Netbook with me on trips, but I wouldn't be comfortable bringing an iPAd only on a trip because it is still somewhat limited (no Ethernet, for one, not everywhere has WIFI and I can't tether my phone to an iPad and get internet access).
I still want one though.