I've been enjoying my Air a lot since I got it on Monday. I went from a MacBook1,1 as my traveling companion (and this is a loose term -- includes my commute) to it. Basically everywhere I go, my laptop is with me; work, vacation, business travel, restaurants, bars, etc. Being that the MB is a first gen model, the MBA feels marginally faster, even if it does not actually benchmark so. Certainly, the MB does not have as much performance as the MBP, so I do not feel I am missing so much, and may not be, aside from a few pounds and an optical drive I rarely used.
With that said, it's hard to say whether or not a MBP to MBA swap is a doable thing. I've entertained going to a MBP before, and primarily for the graphics card. What's stopped me time and again is size.
As for applications... for me, the one thing I think I won't do on the MBA is do my coding (I mess with large compiler stuffs). I don't have a rational reason either, aside from some vague worry about disk space. I have 25GB free on the 64GB disk... I'm not in bad shape. I did take the liberty of removing all my usual transcoding/authoring/editing software this time. Not something I'm keen to do on the go, upon reflection. Aside from iPhoto (which I did keep), I rarely pop open anything "creative" away from the Mac Pro.
Slimming down my MB's contents to fit on the MBA was rather amusing. I forgot I had a /opt from MacPorts, so... I ended up crashing the Migration Assistant... It didn't seem to transfer /opt and /Games, so no biggie. The only game I wanted was WoW. Oh, and while I have installed WoW, I haven't actually tried to log into Shattrath with it.
I guess the upshot of all this is -- purplewarlock, it sounds like you've made a clear analysis and it does sound like the MBA can be a good fit. The only thing that may be iffy is that you want to use the MBA as an only computer, which... (personally) I suspect can be a difficult proposition without some careful thought. I find myself saying "it's OK, there's always the Mac Pro" as a fallback, a bit. It may also be that the Mac Pro is incredibly fast, so I don't try to make things work within the MBA's constraints. I also haven't had the machine long enough to know. "A month without the Mac Pro" IS on my to-do list sometime this summer (thank electricity bills...). I might try it with the MBA (was planning on the Mac mini).