I was in the market for an Ultra Light laptop since I was tired of lugging mine around for 3 hours everyday. I have never been a huge Apple fan so I looked at the Asus ZenBook but it maxes out at 4GB of RAM, I looked at the new Lenovo carbon fiber ultra book but it was hundreds of dollars more expensive. I checked out a few other UltrBooks but they all just looked and felt cheap.
When the new MacBook Air's came out I weighed the pro's and con's, sure the RAM is not replaceable but neither is the RAM on the ZenBook and the MBA can take 8GB. The HDD will eventually be upgradeable whenever a third party makes one and the battery is much more replaceable than the Retina MBP. The USB 3.0 supports SCSI over USB protocol and there are a number of other hardware advantages. Although I wanted to punch a hole in the wall when I had to buy a Thunderbolt cable for $50 0_o, there is no reason they should be that expensive but that is Apple pricing for you.
Coming from Linux it took me a while to get used to OSX and its limitations but overall I am pretty happy with my purchase and would make it again. You can't find an UltraBook for that price with the same specs and build quality.