There are other problems with smartphones that we can't do anything about: connection problems. I often use my smartphone when I'm out and about, to check prices, to find a place to eat/shop, to get the quick answer to a question I just thought of, etc. But I'm in an area with poor reception, so very often I just can't load the sites I want to load.
And even if I can load them and see clearly that they have something I want to buy, interacting with an https section of the site can be a nightmare on a smartphone, so I end up just emailing the link to myself to open on my home computer later. In these cases, I'm probably a zombie visitor... but I often end up buying later from my home PC.
I don't have an Ipad, so I can't speak to that. But I wouldn't write off mobile visitors as useless just yet. The devices need to improve some, and so do connections. But every mobile visit is still an opportunity to, at the very least, impress someone enough to make them want to visit our sites on a regular computer.