I use my retina macbook for everything, and have not found myself using the dell at all, even when traveling. I didn't consider bringing it because I like the Mac so much more.
It is really nice hardware, with the exception that the screen has a much narrower viewing angle than either my macbook or my wife's macbook air. Also the trackpad is not as smooth as my macbook's, and more frequently registers the wrong kind of click.
Ubuntu has worked very well, and seems to be completely supported.
I greatly prefer the mac hardware, and would recommend an Air over the Dell.
edit: since parent disclosed that he got 20% off, I'll disclose that I was very fortunate to receive one for free at a conference raffle.