Seeing incorrect spelling in computer print all the time detracts from the visual image of the correct spelling.  I'm not sure if everyone uses that sort of spatial relationship and image to recognize words, but that's a big part of how I do it.  It's a visual gestalt of the word and not a remembered sequence of letters.  If I'm wondering about the spelling of hand-written words I just recall the print version to see if I've got it right.

Or at least I used to.  The change toward online media has created a situation where everything can have the "in print" glamour of correctness, no matter how ill-informed or tawdry.  Now that everything is hard text online and full of errors, yet still set in "official" looking type, it seems more difficult to just see a word and know if it's correct.  Or it could be age.

And it’s not just spelling, but also basic grammar and usage.  I see this all the time in the debased language on internet forums.  Their there loss has surely exceeded they're gains.  It's not limited to the internet though; any "official" seeming source can push this creepy plasticity into the language.  Have you wondered lately if the correct pronunciation is nuclear or nuke-u-ler? I'm afraid the latter is starting to catch on.

This doesn't seem like a trivial twist in the development of language, driven by the explosive changes we've witnessed in the reach of all forms of media.  I expect it will have a long-term deleterious effect.