Why does source code have to be shown in fixed width? I've been using non-fixed width fonts for about a year now and I find it much nicer on the eyes. The only downside I've found is that sometimes things don't line up quite as nicely, which is purely cosmetic.
My solution to the things not lining up nicely was to give up column alignment completely. In fact, I did that long before I started coding in proportional fonts. I think it was giving up column alignment that opened my eyes to the possibility of using proportional fonts at all. If you don't use column alignment, code looks pretty much the same in a proportional or monospaced font. BTW my favorite coding font right n…
Don't recall anything specific that got me to change back, but change back I did in the end. Just a bunch of small things adding up, really, a combination of limitations in commonly available tools, and the repeated need to print nicely-formatted tabular things to the all-pervasive monospaced text console. Swimming against the tide just ended up being more hassle than I felt it was worth.