The 11" is desirable and I was tempted by it, but the 13" has its place. I'm doing a lot of Lightroom and Xcode with it, so the extra screen real estate is significant there (and man does it blaze through RAW image previews thanks to the SSD!). And the at most 5 hours of battery life on the 11" is just not quite enough to get through a typical day, and I hate that feeling of having to be near an outlet and bring the plug with me at all times just in case. The extra 2 hours on the 13" is just enough to tip the scales the other way. Also like the larger trackpad and the SD card slot.
And while the 11" is incredibly small and light, the 2.9 lb. 13" feels like nothing after coming from a 5.5 lb. 15" MBP. Both are great, but I'm glad both models exist. That said, if they made a single model instead, right in the middle, let's say a 12.5" screen with 6-hour battery life and 2.5 lbs., it would be just about perfect for me.