Proportional is still very contreversial. A few of us have made the transition, and won't go back to fixed-width, but many value the ability to do ASCII art (aka space-based alignment). Other than that, there is absolutely no advantage to using a type writer font on a modern display.
I've been using a proportional font since the beginning of the year. It took one week to adjust (things look weird for a few days).
I tried the Input font time ago and didn't like the way it looked, but maybe I have to fiddle with its settings and find a way to make it look nicer. I'm using DejaVu Sans inside emacs now. The only shortcomings with the font are that l (lowercase el) and I (uppercase I) to be indistinguishable, but it's rare that they cause trouble. Uppercase o and zero are distinguishable (zero is narrower), but maybe a marker inside the zero would be handy. Not sure about that. Context usually is enough to make them apart.
Overall a page of code formatted proportionally is much nicer to look at than a monospaced one, so I'm not going back.
It would be nice for editors to support alignment with proportional fonts inside lines (see http://nickgravgaard.com/elastic-tabstops/). Maybe this is not going to play with Python and similar languages but automatic transformation of spaces into tabs and vice versa has been around for years and we have more CPU cycles than we need now.
