[Avodah] shinuy on Shabbos

[David Riceman]

  Another question from my son.  We were talking about why the Rabbis 
proscribed doing melachos on Shabbos with a shinuy, and I suggested that 
once it became common practice it would no longer be a shinuy and would 
be Biblically prohibited.
  Are there any actual examples of something that was once a shinuy and 
is now standard practice in the context of hilchos Shabbos?

David Riceman