I'm at the edge, ready to jump...

I too am jumping back and forth between a refurb/used 2011 MBP 15 or a brand new MBA 13. I love the style of the air but I need a 512 SSD and that is just to much for me. For under 1400 dollars you can get a 2.2 quad, 500GB and 4GB of ram. You can add a 128 SSD by eliminating the superdrive around 150 dollars. So you have your apps on the SSD and all your media on your HDD. So for 1500 dollars you can have an amazing setup. Just my 2 cents.

I was in the same position, IT professional who also has started dabbling in programming. I have been preparing to buy a MacPro for months. I was waiting for WWDC though, and when I found out the Air's were now able to have 8GB of RAM, I bit.
The only problem with them is the limit on HD space, but the SSD is so fast and with SD card and USB 3.0 (and if thunderbolt ever gets afforable for storage) Their are plenty of ways to get around that.

Its hard to beat for the price when you consider the performance your going to have combined with the portability.

I work as a web developer and have been working on a late 2008 13" alu macbook (2.0GHZ, 4GB, 160GB) which was capable of doing everything I needed it to. The only issues I had with it was slowdown when I had a large PSD open in photoshop or a bunch of tabs open in firefox (I ran xcode a couple of times for the iPhone emulator and it seemed to struggle there too with a bunch of other apps open). It started playing up a few months back so with the impending refresh decided to upgrade. I had my mind set on a new MBP but always liked the air so convinced myself that this was the way to go. In the end, I sprang for a 128GB 13" 8GB air. The way I see it, my 4yr old machine was pretty capable and this will likely be 3X as powerful so no issues with this for a few years, plus I travel quite a lot and in my current job I cycle 5km each way to the office so will be nice to have less weight on my back. I will have to dance around the small HD though. It left Shanghai yesterday.