Perhaps it's appropriate to mention that popular usage by
somewhat-literate people who either don't read much, or don't perceive
actual spellings, has a loose consensus about variant spellings (OK, call
them wrong).
I refer to it as a developing written dialect that might be graciously
referred to as Popular English, perhaps by analogy with Vulgar Latin
(something I don't know much about). Perhaps it's unfair to say that
incompetent teaching of English is responsible; teachers have too little
respect in the USA. While I don't expect to see this popular dialect used
for articles in, say, The Atlantic Monthly for decades (I'll be gone...),
nevertheless, in e-mail and other personal usage, it seems to be quite
common.
One of the easiest words to note, I'd say, is "alot"; many people think
it's a real word. ("Napple/apple" is an historical counterexample.)
"Its/it's" confusion needs no introduction; a word-processor search for
"it's" and replacement with "it is" is likely to create some
absurd-looking text. It seems to me that there's a trend toward always
including the apostrophe. This confusion is a pity, because it seems to me
that only a few minutes of classroom time is enough to explain how to
spell these (and why!); reinforcement and reminders ought to teach it
successfully.
"Than" and "then" are in a state of confusion; I've seen numerous
instances where the word "than" is intended, but spelled "then", as in
"more then enough". The reverse, using "than" where "then" is meant, seems
to be significantly more uncommon. Finally, concerning these two, "than"
is becoming a "general-purpose connective"* that has very loose syntax.
Its virtue, once one recovers from the very distracting usage, is
conciseness; used in this fashion, it can replace a whole phrase that has
a somewhat-convoluted syntax.
*my recollection of grammatical terms is quite poor; sorry!
Some other forms, such as "accidently" seem to follow speech, as well as
show little concern for awareness of basis words (accidental, in this
case).
However, a whole category that really disturbs me is omitted middle
syllables, a topic I commented on some time back. When a small storefront
business has to close temporarily and unexpectedly, it's quite likely that
the temporary notice on the door will say "Sorry for the inconvience." A
few more such are "nutrious", "incandent", and "sectary". I did compile a
list of actual instances of these words, although it's in limbo (or lost),
pending recovery of a damaged archive partition.
Why these squeezed words are accepted and written seems to be related to
methods of teaching reading, as well as various ways people perceive
printed text. It seems that they regard the beginnings (and sometimes,
ends) of words phonetically, but there must be a strong element of
teaching as whole words, as if our language were logographic.
Wandering off-topic somewhat, I'm pained to witness a tragic level of
illiteracy among intelligent, otherwise-literate younger people who are
almost desperately baffled by trying to pronounce unfamiliar, simple,
straightforwardly-phonetic words such as "Ubuntu". Another such word was a
trade name, "Yodolo". They are stuck at about second-grade level (even
though some have college degrees), and to hear them mangle such words
hurts. They simply do not progressively look at syllables, pronouncing
each in sequence; they seem to be fanatical about regarding the word as a
whole, and it just doesn't work.
A while ago, I worked for a Fred Murray, and have a neighbor named L.
Swain. Both these people assure me that their surnames are too difficult
for many Americans to spell or pronounce. Now, I don't expect them to
quickly and fluently deal with the likes of Przemyslaw Prusinkiewicz or
Mihaly Csikszentmihalyi, but, good grief, Murray and Swain?
One younger computer programmer, with a well-organized mind, absolutely
refused to try to pronounce any word in print that he had not heard spoken.
Finally, even among those who are excellent spellers and who write
literate English, the two verbs "lose" and "breathe" are frequently
misspelled as "loose" and "breath" -- but only by those born after WW II,
roughly; why it's generational is a big mystery. The spelling
inconsistency between rhyming words "lose" and "choose" is worth noting .
(As to age, I'm threescore and ten and some months more, fwiw.)
Interesting that "score" suggests a radix-20 scheme of counting. It might
well have developed in a warm climate!