Bingo. I work at a command line all day, and even use the "Terminal" GMail theme with plain-text formatting. I'm glad someone else recognizes that monospaced fonts are a hallmark of nerds.
Now that it’s established, of course, we’re all pretty much locked in. Most of the text on my screen right now is monospaced. I mean, good luck writing code in a proportional font: pretty much every language and text editor assumes you can align with spaces, tiny punctuation looks huge, etc.
But saying that monospace is inherently nerdy is like saying that, say, slashes are inherently path separators.
Monospace isn't entirely an accident.
I could complain the same way about practically anything. Cement. Unix. C. The genitive absolute. But granted that great things are made out of hacks, some hacks are uglier than others, and monospace is pretty darn ugly.
C is an overgrown assembly language, and Unix doesn't have enough kitchen sinkery going on to make all of the tiny programs that do one thing well even marginally useful.
iTerm and TextMate can't handle variable-width fonts, which makes me sad. At least I get my pointy serifs with CentSchBook Mono, though.
I work at a command-line all day but the 'Terminal' GMail theme makes my eyes bleed. :(