Do you not understand how misusing a homonym that even my 4-year-old understands (no exaggeration) makes one look like a simpleton?
I mean, how does a fully-functioning adult expect to be taken seriously as a poster if they can't utilize basic elementary spelling skills? And, conversely, if one doesn't expect to be taken seriously, then don't get upset when one's posts are dissected.
I know that when I see a post rife with spelling and grammatical errors, I pretty much discredit anything the poster has to say from there on out. Whether you want to believe it or not, proper use of communication is a sign of intelligence, and someone who can't use basic words properly either has a learning disability or is not very intelligent.
And, while I do realize that we are on an informal message board, misspelling basic words like "then/than" do not fall under the umbrella of "internet slang" or whatever moniker you wish to use.