I have tab and column alignment OCD. I can't even read other people's code without getting a terrible itch to realign things. I think a proportional font would either drive me crazy or, on the other hand, might be kind of good for me.
It's the dirty little secret of the "we hate tabs crowd" - they have to keep everybody in monospaced fonts otherwise their conspiracy to force programmers to repeatedly bash their space bars falls apart.
All joking aside, the choice of font should reflect what it is that you are trying to do with the text.
In theory a serifed font is more readable if you are reading the entire text, whereas a sans serif font is supposedly better for skimming through looking for something in particular.
(so on a web page with an article, the article text should be serifed, and the sidebar menu should be sans serif)
An application of this might be that if you are printing out a codebase in order to read it in entirety for the first time, you should use a font with serifs.
whereas if the codebase is relatively familiar to you, but you are printing it out and going bug hunting or reviewing the code, use a sans serif font.
