My previous rig: I have been using a dell xps studio 16 as my main laptop for the past year. It has been awesome all the way. It cost only 1100$ and came with impressive specs like a quad core CPU and 1GB dedicated GPU. I primarily used Visual Studio 2010 and develop in .NET.
Like many people I feel that it was time I tried the "other" popular platform that users were loving. The Mac/iOS family. I would like to point out I already use iPhone as my main phone. I also have an iPad which resulted in an explosion in the amount of reading I got done in the past 2 years. Simply because of the ease of closing one book when I no longer feel the author or feel overwhelmed with the information and opening the another one instantaneously.
But I have never owned or even used a Mac before. And that just feels not right for a geek. The reason why I never bought one before was two fold:
I live and breathe C#
No longer an issue thanks to Mono guys. http://xamarin.com/
I am an engineer and appreciate code beauty and code evolution. C# satisfies my urge for programmers lives being made easy by other programmers. If no ones lives are getting easier programmers aren't focusing on the right kinds of problems.
I like the freedom of hardware choice
Still an issue. But unfortunately there are some major discrepancies in my windows hardware : The webcam on my dell was not the awesomest. But more importantly : There is a delay when I try to record and live listen audio plugged into line in. Even my P2 desktop didn't have this problem. Compare this with what mac gives you : http://www.apple.com/ilife/garageband/ Being a (hobbyist) musician having a system guaranteed to work (like all apple products) as advertised is a safety that I enjoy over mix and match hardware choice.
I never put the Dell XPS studio 16 on my lap because of known overheating and motherboard frying incidents. And didn't even move around with it much because of weight and because of fear of a harddisk crash.
The macbook air is the best ultrabook you can buy right now. And the 11inch, 128GB SSD, 4GB base version is comparable in price to windows ultrabooks.
In short Macbook Air is the best "laptop" you can buy. You can make yourself a better desktop. But a better ultra-portable laptop is impossible to make on your own.