No tablets, not ever. I can't think of anything they can do that a real computer or a smartphone couldn't do better. I've never seen the point beyond very specific specialized uses.
I've had iPads since day one, and I'm at the point where I'm seriously considering not replacing my laptop and doing all my mobile computing on the iPad. If I need a real computer, what I really need is a desktop with a big screen, lots of power, and much better ergonomics than a laptop. Anything short of that the iPad can do what I need, in a package that's a lot easier to use while away from the desk.
I guess for me, the smartphone has become the default for my mobile computing (beyond normal phone-exclusive tasks such as calls, messaging, camera, GPS, etc.). I can type out a quick email, look something up online, or update a Google Docs spreadsheet if need be. It's not as nice as a laptop for doing any of those things, but it's way way more convenient to have it in my pocket vs dragging something like a laptop or tablet around.
A tablet could do all of that, but not much more, at least of what matters to me. The closest to a useful tablet I've seen is Microsoft's Surface Pro series, since it runs actual Windows, but even that seems like way too expensive for what it is.
If I need anything more than my smartphone, what I really need is a laptop/desktop. And what I find myself needing is either an actual window manager, multiple monitors, real apps running on a real OS, a lot more power, or a real keyboard. I can only type 30wpm on my phone, and not comfortably, while I can do 110wpm all day on a desktop keyboard (tested both just now online). And even a shitty trackpad is better than any touchscreen.
My laptop rarely leaves my house these days; it's basically a backup for if I want to use the computer and my girlfriend is already on the desktop.