Seth Godin touches upon the importance of what you convey online, by way of how you write.

Poor (/lazy) spelling and grammar is especially annoying when the writer is trying to speak authoritatively or in an impassioned form. Two of my personal faves:

rediculous

rediculous

and

definately.

(Check out www.d-e-f-i-n-i-t-e-l-y.com)