Not only does misspelling bother me, so does incorrect grammar and slang. Nothing puts me off reading something more than incorrect spelling or slang terms. It shows me that the author is not diligent enough to make sure their work is the best it can be. To me, it also shows a distinct lack of concern over the quality of their work.
If the work I'm reading is non-fiction, I immediately begin to suspect the veracity of the facts because I feel if they are that sloppy about spelling, grammar, and slang; then, their fact-finding skills are probably in the same class.
There was a time when writers had pride in their work.