More than three pages and nobody has mentioned:
weiner/wiener
yet.
your all weiners, not loosers.
What’s a heat sync (the thing you have on your computer’s CPU)?
Also, not so much a misspelling* but using the wrong word (as in the OP): effect and affect.
*Of course, they are the same except one has an “a” and the other an “e”, but I see people consistently reversing them (“What affect will this have?”, “This won’t effect me”).
Some others, like imposible, where a double letter is replaced with one.
Also, isn’t diarrhoea supposed to be spelled diarrhea (Firefox underlines the former spelling), same for words like aluminium (aluminum)? 
These are more often usage errors, rather than spelling errors. For example, using “bazaar” when “bizarre” is meant. Both are correctly spelled; however, they are misused.
phase/faze
Not if you’re British.
Tie-dyed, I hope. I’m in need of something colorful, after three straight days of mist.
Y’all is a contraction of “you” and “all”. The apostrophe means “some letters have been taken out”. When you go from “you all” to “yall”, the apostrophe does not go after the a. Unless ye’re one of those wierdos who write you as ya and have an assassin in your makeup bag, that is.
I would blame English. And it is unfair to judge English speakers severely because some languages are spell-friendly but English is not.
Moreover I don’t understand why you are angry at people’s mistake. Let them know they are misspelling and leave it there. If they correct it and improve themselves, it is their benefit. If they don’t do so, that’s their loss.
Thanks for that.
That’s what some people do, ya know.
nm. Just saw my example upthread.
I have two.
One is “donut” for “doughnut”. I guess it’s an acceptable spelling, but it just strikes me as trashy, somehow.
This is one I’ve seen lately - “Bokay” for “bouquet”. WTF. That’s horrible!
And that’s the reason I wish Firefox had an easy way to delete words from its spelling dictionary (without having to go edit a text file as an administrator). I always try to delete words where the misspelling is more common than the esoteric word. I mean, if anyone is going to use the esoteric word, isn’t it quite likely that they know the correct spelling?
I recently saw “ya’ll” on a local billboard.
I also saw a sign advertising a local business (in Alabama) which said that the owner was “Bama born and Bama bread.”
Another one that I occasionally see is “birth” instead of “berth”. Example:
The team earned a birth in the championship game.
The correct word in this instance would be “berth”.
Words in my experience (proofreader) go thru “spells” of misspelling, and sometimes all it takes is for the word to become more widely used for the misspelling to go away.
I remember when “harrassment” was everywhere in the 1980s, until the word was common enough in print to almost always lose that extra “r.”
But, sometimes, a misspelling of a popular word simply comes and goes and, more often than not, comes again, for no readily apparent reason (“cemetary,” " Edgar Allen Poe")
I thought “donut” was the usual US spelling. Here in the UK (where “doughnut” is standard), that spelling is sometimes used to lend an American-style impression.
I notice a huge number of such homophone substitutions in my own writing, as well as sometimes in other Dopers’ posts. And I’m not a particularly poor speller – I even won(*) spelling bees … 50+ years ago.
(Just now, as I wrote “won”, I actually typed “o^Hwon”, that is, I started to type “one.” That I caught this homophonic error after only a single letter may be because it’s the topic of the post! I also wrote “thought” for “though,” caught on Preview.)
I think that my brain has some poor circuitry between “audio vocabulary cortex” and “keyboard typing cortex.” I wonder if I’d have similar problems with hand-writing, but do far too little handwriting these days to check.
That one I can remember!
I before E
Except after C
(Or just to be Weird) 
This applies to me. There are a few words where I seem to have memorized the fact that I misspell them. Even if I spell them correctly, a perverse imp will pop into my consciousness reminding me I “should” be spelling it incorrectly. :smack: