I have multiple tablets and a netbook, having given up a full desktop machine years ago.
I love tablets. But the netbook is a much better prospect since it can serve as both a desktop machine (mine docks to a keyboard, mouse, external monitor and a couple of external drives) and a mobile device. I run linux on mine because it runs well. There are two more netbooks in the house with Windows on them, and I find them to be a total chore to use. I'm the "lucky" person who ends up having to maintain them, too.
I use the netbook when I'm going to be someplace for long enough to sit and do real computing. When time or conditions don't accomodate that very well, the tablet is a great alternative. But it could never be my primary device. Not as they exist now.
The tablet is wonderful for quick notes, GPS (better than my phone and the dedicated GPS I have), videos (making and watching), price comparisons (which the phone can also be used to do), playing games and quick forays onto the internet. It would be wonderful for handwriting recognition, which could eliminate partially the need for a keyboard. But mine all have capacitive screens, and the only pen I could find that would work was almost as fat as a fingertip. I may buy a resistive screen model to see how well that works. In any case, the touchscreen alone isn't good for having to type large amounts of data. Predictive text helps with that part, but there's still the problem of key sizes and proximity. A keyboard attached in a case to hold everything can be a bit clumsy when the keyboard itself is not being used, which is most of the time in my case. So the tablet I use most doesn't have one. My son's, the same model, does. I don't think I've ever seen him use it.
I can video chat. I don't do it much, but I do it. I use Skype sometimes. Both require a decent connection, of course.
I use 7" tablets. I find the size is perfect for fitting into the pocket of cargo pants, it's just the right size to hold with one hand while working with the other, etc. The downside is the on-screen keys are closer together than a larger tablet. But I honestly don't think I'd do any more typing on a larger screen than I do on the 7" models. A keyboard/case on the 7" tablet is about double the bulk. That's probably true of many models with larger screens, too.
Whether or not someone could use a tablet as a primary connection depends on how they intend to use it and the capabilities of the tablet. Many people use their phones for everything. Those could get by much easier with a tablet. But I could never do that, not with today's designs and capabilities.