I realize it's a different story for others, but in my opinion tablets are the redheaded stepchild of the current lineup. Desktops obviously are perfectly viable. Laptops (including netbooks for sure) I see as very viable as well, as the mobile solution with a keyboard and a non-phone-sized screen. Then smartphones are perfectly viable as well, since they are small enough to fit in your pocket.
Tablets don't really fit in any sort of conventional pocket, can be awkward to hold for extended periods of time, and to me seem like an unnecessary bridge between a smartphone and a netbook/laptop. Netbooks are in the same league of mobility as tablets, are more powerful, have keyboards, more features, and are a lot more comfortable to work with. Things can always change, but this is the way I see it in their current forms. Tablets are just...redundant. Not to mention user freedom. Many/all tablets are a walled garden of one sort or another.
The one big plus tablets have over netbooks/laptops is the battery life. You can come close to matching an average tablet's battery life by purchasing a better battery for some models of netbooks, but they can be hard to find.