Definitely check out this thread. It gets a little long winded and devolved into a discussion on linguistics, but this you can expect from this forum.
In short, I’m extremely pleased I went with the 11" because the main thing I was looking for is ultra-portability. It is literally in the netbook class, whether or not you want to call it one is a matter of not calling a 4-door BMW a family car, I suppose. At only a little over one inch longer than an iPad, and roughly identical in dimensions and weight otherwise, it’s the type of thing you will swear you forgot to bring based on the weight of your bag, and then realise you did bring when you check.
I think performance is a bit of a moot point with either of these. Both are definitely not high performance machines, and they are between each other only shades apart. Really, the differences are minimal. What you are getting with the 13" is a bigger screen. The only way you’d really detect any performance difference between the two is if you are really pushing them with Photoshop or some other intensive tool—and then if you really need that, it’s probably not the best machine for the job—either of them. From the checklist you provided, I don’t see anything that will be a negative on this computer. I’ve only played one game on it, A.I. Wars, which is fairly CPU intensive and not terribly GPU intensive. It had no problem with it. I think I recall Keith reporting that Adobe CS4 (or 5?) stuff runs way better than expected. Another point on performance is that this isn’t really going to scale as much as other purposes might. If you are in video, graphic design, or just even a gamer, then shooting for the best gear of the year so you can get three years out of it is a necessity. For a writing machine though? The software out there for writers is all low-impact. You can save entire libraries on a modern drive. For a writer, even a standard spec computer can last as long as the parts keep ticking. We still have people using Scrivener on old G3 and G4 computers, believe it or not. Even though these machines are not high end, they are very fast for their class, fast enough to be compared with a class or two higher in the “overkill for writers” area. So my estimation: easy three years… no problem. I’d say six to eight so long as the parts last. This is why I don’t think there is much of a difference between the two models in this realm. They are both about the same for a low-impact trade like writing and both will probably remain computationally effective for longer than the sum of their parts. Form factor will be the big decider. You get more screen with the bigger one, but its going to be more like having a laptop; you’ll need a more standard sized laptop bag. You get less screen with the 11", but its barely any larger than a trade paperback and no heavier; you can fit it into many purse or small hip bags that aren’t even meant for computers.
In some areas, they have fantastic performance. In fact for disk heavy tasks, it handily outperforms my 2008 MBP 15". There is much behind the numbers on either of these computers. They are highly optimised, and that solid state storage does a number on some tasks. I bet DTP works good on it too, since that’s a file heavy program.
Screen size is a mixed bag: depends on your eyes I would say. Fonts will be much smaller than you are used to. 12pt fonts will look more like 9pt fonts—but this is because of pixel density, which means even though they are smaller they are just as crisp and legible as 12pt fonts on a regular screen. To my eyes, the screen looks very close to your typical budget laser printer, text is amazingly crisp—but if your eyes aren’t so good at near stuff, you might find you need to use text zooming features a bit more often than you otherwise might. With both computers, because of this high density, you get more space than you’d think. Scrivener feels very comfortable to me on it, despite being so small. It really feels more like a normal 13" screen to me. The ultra-widescreen though—that’s going to be its biggest area of frustration, especially for writers which would prefer to see more text on a “page”. Someone posted a shot of the MBA set up sidewise like a book on the desk with a BlueTooth keyboard and screen rotation enabled. 
Battery is good. With all antennas off and the screen dimmed, I can get about six to seven hours of usage. That’s writing and editing, nothing more fancy than that. With the WiFi on and browsing around, that’ll drop down to 4–5 hours; far less if you visit a site with Flash (I recommend disabling it in the browser). Six or so hours of practical usage is more than I need. I usually just take this thing to coffee shops and the library, and I’m rarely in one or both of those places for longer than that.
Regrets? None. I’ve said it before, but it’s the best laptop I’ve ever bought—with the '08 MBP a close second. It’s perfect for what I wanted, a super portable writing machine that lets me write instantly whenever I have an idea and close it up just as fast. Because it is solid state, I can just snap the lid and instantly stow it. You can’t (or rather you really shouldn’t) do that to a regular laptop because it needs to park the drive head first and that can take around 10 to 15 seconds. In terms of immediacy, it is right up there with the iPad; just pull it out, use it, stow it.
