Something like the shift in meaning of 'literally', that many people are complaining about, but has a good chance of taking root and becoming the norm in the future. Are there recording instances of similar criticisms being made in English, Latin, French, Spanish, or Italian (or other romance languages)? Can be orthography, pronunciation, or grammar. Some example that would be of particular interest: the loss of final vowel/consonant pronunciation in French, dipthongization of stressed vowels in Spanish, use of do-support in English.
The Appendix Probi provides quite a lot of information about changes from the Classical period to the 3rd century. We see a lot of evidence of vowel reduction in unstressed syllables. For instance, "speculum non speclum" with a vowel lost entirely; "vacua non vaqua" with /u/ changed to /w/; "formica non furmica" with /o/ raised to /u/. I'm certain this isn't the oldest evidence of peeving (although it's fairly thorough).
When... did "literally" change meaning? Did I miss something?