Common usage by people who don't know better does not make it acceptable grammatically.Then they would be wrong.
! You are swimming against the tide here. Although misplaced apostrophes, which make text difficult to understand, are a pain, I am quite relaxed about you and me using you and me
rather than the terribly affected you and I
and it's I
. I am not so sure about uninterested
though, nor affect
but I guess those battles are already lost.
As for common usage, there are enough examples of common usage becoming accepted grammar already, and this case is already lost. Do you want us to revert to, what?, Latin?, Anglo-Saxon?, Norman French?, Middle Ages English?
We users own the English language, not the Queen, and certainly not some rulebook frozen in time. The rulebook is a total mess already, with all its exceptions. Just make a new exception: It's me
is acceptable and correct.
As for Lynn Truss, I disagree with many of her arbitrary rules. I am not going to try to stop her writing that way, though!