What's a MacBook Air good for?

At the beginning of this year, I bought a MacBook Air. I bought a maxed out one, with a 13" screen, 2.13 GHz cpu, 4 gb ram, 256 gb SSD. This past week Apple refreshed the MacBook Air line and I've seen a lot of people asking the question "Could I use a MacBook Air for ___?" So here's what all I use it for, along with a comparison to my work computer a maxed out 15" MacBook Pro.

• Web browsing. I run Chrome on it and it screams. Actually the MBA set an expectation for me about how ChromeOS and in particular how my Samsung Chromebook should perform. I basically expected the Chromebook to perform exactly like the Chrome browser on my MBA, which is awesome. I was very disappointed, as the Chromebook is nowhere close. Anyways, browsing on the MBA is fantastic. I can notice a slight difference in performance on super-JS heavy sites, with my MBP being slightly smoother. I think a non-engineer would have difficultly spotting these differences.
• Word processing. I'm not just talking about rudimentary word processing either. When I got the MBA, I had a couple of chapters and appendices that I was still working on for Android in Practice. I used the MBA to write/complete these chapters. This involved using Microsoft Word along with the Manning Publications template for Word. The chapters were usually in the 30-50 page range, and often with tons of formatting (code, sidebars, etc.) and large graphics. I cannot tell any difference between my MBP and MBA for these massive Word docs.
• Programming. Speaking of AIP, part of finishing it meant writing code for those chapters. I've run pretty much all of the code from AIP on my MBA with no problems at all. For smaller apps like I have in AIP, there is no appreciable difference between my MBA and MBP. Building a small app is an I/O bound task, and the SSD on the MBA shines. Now I have also built Bump on my MBA, and there is a very noticeable difference between it and my MBP. There are two major phases to the Bump build. The first is the native compilation, which is single-threaded. You can definitely notice a major CPU speed difference here, even though the raw clock speeds of the two machines are close. The second phase is the Scala/Java compilation phase. This is multi-threaded, and the four cores on my MBP obviously trump the two cores on the MBA. Still, I would saw the MBA compares favorably to the late-2008 era MacBook Pro that I used to use for work.
• Photography. I used to use Aperture on my old MBP. On the MBA I decided to give Adobe Lightroom a try. So it's not an apples-to-apples comparison. However, Lightroom on my MBA blows away Aperture on my old MBP. I haven't tried either on my current MBP. Obviously the SSD makes a huge difference here. Nonetheless, post-processing on the MBA is super smooth. When it comes to my modest photography, Lightroom presents no problem for my MBA.
• Watching video. I haven't watched too much video on my MBA, mostly just streaming Netflix. It is super smooth, though it will cause the machine's rarely used fan to kick-in (as will intense compilations, like building Bump.) Next week I am going on a cruise to Mexico, and I will probably buy/rent a few videos from iTunes to watch on the cruise. Based on previous experiences, I expect this to be super smooth and beautiful, though I have considered taking the MBP just for its bigger, high resolution screen.
• Presentations. I've done a couple of talks using the MBA. For creating content in Keynote, I do sometimes notice a little sluggishness on the MBA that is not present on my MBP. For playback, it seems very smooth. However, I did have an animation glitch during one presentation. This never happened when previewing just on my MBA's screen, it only happened on the projected screen. Nobody seemed to notice during the presentation, except for me of course.

So there you go. What's a MacBook Air good for? Pretty much everything. If you are a professional developer who compiles software, then I think your money is best spent buying the most powerful computer available. This has always been true. Maybe this is also the case for professional photographers/videographers as well. However my MBA is way more than enough for most folks. Finally keep in mind that the new MBAs introduced this week are a good bit faster than my MBA, at least in terms of CPU speed.