In this post I just wanted to quickly document two items I came across recently.
The first is the substitution of "upmost" for "utmost". This fits the classic definition of an eggcorn: mistaking a particular turn of phrase for a phonologically similar word or phrase that makes more intuitive sense. When we talk about something "of the utmost importance", we mean something of the highest import, something that should be at the top of our list. Thus it makes perfect sense that some people would reanalyze "utmost" as "upmost", especially given that the stops are in coda position next to a bilabial /m/, making the phonetic distinction between the two probably very slim. This substitution seems to be fairly common; I got almost 5M ghits, and the top one was an article called "Don't Confuse 'Utmost' with 'Upmost'", hosted on a site related to grammar tips. COCA only returns 8 results, not all relevant, but given that "upmost" is most likely to occur in speech, and transcribers may simply hear "utmost" since that is the standard, most likely there would be significantly more results.
The spelling pronunciation I came across recently is "half to". While not an eggcorn ("half to" makes no more intuitive sense than "have to", in fact I'd say it makes less sense), I still find this interesting. Most likely the writer here is thinking of the fact that the word 'have' contains a /v/, and since the /v/ in "have to" is devoiced (obligatorily, at least for me), "half to" more accurately represents the phrase phonetically. Voicing the /v/ in "have to" sounds quite archaic to me, and primes constructions like "I still have homework to do" much more than the relevant meaning "I am required to X". Unfortunately constructions like "one and a half to two" and "half to death" make it almost impossible to turn up genuine results of this online. A similar situation obtains with "supposed to": if you tell me you're "suppo[zd] to do" something, my first thought is that someone's making a supposition about you, rather than giving you a requirement. The devoicing here is so necessary in my idiolect that voicing the final cluster sounds like hypercorrection to me. The spelling "suppose to" again seems very common: almost 7M ghits, with several grammar sites warning against this "mistake". COCA actually turns up some instances that seem to be genuine as well. This type of phonological reduction is common with set phrases, and I'm guessing is assimilation in voicing to the following /t/.