I haven't used my Air since getting a Pixel. When I need to build something, I fire up Sublime in VT3.
Fully-featured web IDE; supports Ruby, Python, Go, and more. You provision a box to do your development on.
I know Unity hasn't, and Gnome 3 (my favorite) has pixel-doubling support on the way, but if there are any others or if you've been able to optimize an X WM to be readable and polished.
https://github.com/appsforartists/pixel_webdev
All I use it for is Sublime Text, so things more-or-less look great for me. The problem with Linux is that there are multiple ways of doing any one thing. So, just because Openbox and Sublime can handle high DPI doesn't mean your run-of-the-mill KDE/GTK app will.
I've got my setup scripted here: