So I've got the MacBook Air's HDD replaced and am using it as my primary machine. Expect not for the CAD work which I do on my office PC, with two monitors and ubuntu.
I wish to share my experience from a point of view of a user, rather than a Apple design fan, which I am and which is something which has made my feedbacks on Apple products a bit too biased.
To start with what I use most, the browser, viz. Safari. It's true Safari is fast, and you especially notice it when you are sitting on a fat internet pipe with over 1 Mbps speeds. Its simple and does most of the work done. But there are those idiotic activeX pages, which won't load. Also I have had issues with even Apple.com not loading on MAC-Safari pair. I mean come-on!!! The problem is solved by deleting the apple.com's cookies from the browser.
It does get hot, but I guess most modern notebooks do. Not as much as a Macbook Pros, but yes, no "Laptop", please!. There is an issue with placement of the fan in the Macbook Air, it's at the bottom, and it starts to get exponentially hotter when kept on the bed, so it needs a hard surface to be kept for a little more than the casual amounts of work.
Aah and the one USB is a problem, maybe, I feel the need for the second port at work, with no wifi and only LAN, so my USB goes to the ethernet connector. I eneded up buying a USB hub, but that does not power my external HDD, so it's just OK again.
As much as Apple tries to beat down Windows, take my word, Macs also hang. They too have not responding applications. Maybe 1/10th the number of times a well managed Windows machine has it, but applications do hang here too.
I do love the fact that it sleeps nicely with the lid closed, that the battery lasts long enough for most of my work and fancy and useful things like the ambient light sensor adjusts keyboard and screen light. I love it being light, I love to show it off.
Overall I'd say that it has its' own pros and cons and to be true, it "just" overshadows an expensive windows based laptop.