Brent Simmons makes the case that proper grammar and punctuation among coders is important:
This is not, by the way, some prissy thing about proper manners. Fuck that shit. I’m not trying to squash your voice. This is about quality and trust
For better or worse, whenever I see bad spelling or grammar, my opinion of the writer plummets. This is especially true when I see people constantly butcher there, their, and they're. Drives me nuts.
Matt Gemmell offers good perspective on this issue:
Whatever a person’s excuse might be, it’s difficult to get past the idea that this is someone who has failed to comprehend and internalise the rules of a language they’ve used almost every day of their life. That’s the magnitude of the negative impression being created. It’s like publicly, repeatedly demonstrating that you can’t tell the time, or count – and that you bizarrely don’t see those deficiencies as particularly worrisome or problematic.
Point being, this stuff isn't rocket science, folks — don't be lazy. Know your shit.