I've been using the iPad Air as my primary (and pretty much only) iPad since it launched on November 1st, and thought that it was about time that I shared some of my thoughts.
After carrying the first three full-size iPads pretty much everywhere for two-and-a-half years, I'd switched to the Mini full time last year. While for the most part this changed little other than being much easier to carry around all day (and meant I could more often switch to a smaller bag when popping to a cafe for a few hours), the Mini came with a couple of caveats.
Firstly, the screen resolution. In just six months or so of using the third-generation iPad I'd become very acclimatised to the retina display. While I don't wear glasses I probably should, and moving to a smaller, and decidedly lower-resolution screen really irked me, and almost certainly meant I did less reading on the Mini than I otherwise would have. When I did read for any length of time, I was frequently irritated by how much poorer the display was than on the iPad 3, though I comforted myself by occasionally picking up the older device and reminding myself how much it weighed.
Secondly, the screen size. While it's a pretty obvious part of the trade-off in choosing a Mini, and while 7.9 inches is a whole lot more useful than the widescreen 7-inch displays packed by many other small tablets, there are still a fair few websites (and web services) that I use on a day-to-day basis that just aren't built for tablet-sized screens. Some of them are barely usable on the full-size iPad, and using them on anything smaller is to enter a world of scrolling and zooming.
Trying to balance both of these concerns put me right on the border of the use cases for both sizes of the iPad. The Mini's new retina display solves the one issue perfectly, while the dramatic weight reduction (and slightly less-dramatic size reduction) in the iPad Air solves the other. The almost identical performance of the two new devices makes the choice even more difficult (as almost everybody has already written).
In the end, the choice for me came down partly to availability (the Air shipped in good numbers on the 1st November, the Mini is only just shipping and is much more constrained), partly to curiosity (was it the Mini's size that made it my favourite device, or its weight?), and partly to a desire to understand how some of the more desktop-equivalent Apps that have shipped over the last year might change the way I use the iPad. Long story short: I queued up on launch morning and snagged a 64GB Space Grey cellular model.
Much has been written about how significant the weight reduction is with the Air, and I have nothing more to add, other than this: I genuinely can't tell the difference between having the Mini in my bag or the new Air. I imagine that if I was in the habit of only carrying a handbag with me I'd think twice about bringing the Air along, but even carrying it one-handed around my workplace all day isn't an issue. I'm appreciative of the switch to the new-style Smart Cover, which removes some additional weight, and the move to the A7 chip (which the Retina Mini also gets) is yet another nail in the coffin of the traditional notebook computer. I honestly can't think of a situation in which I'd rather carry an 11-inch MacBook Air than this device (though if Apple really has a radically thin 12-inch MBA in the works for 2014/15 I'm betting it looks a lot like the iPad Air).
I'll share more on specific use cases and how I'm getting along as the opportunity arises. One final thing though: When Apple announced the iPad Air, quite a few of us half-expected an iPad Pro to complete the range. I'm still thinking that a larger-screen iPad is a distinct possibility, though—for now—the iPad Air is as close to a desktop replacement as I could have hoped for.