Just now I was washing breakfast dishes and mentally composing a Facebook post, which started out “Last night was not a good night for Orioles – Red Sox – anti-Yankees fans! The three way tie for first place got broken in the worst direction! Us and our Red Sox buddies …” and I forget how that sentence was going to end, because I was caught up short noticing how it began. I’ve known about the ongoing spread of the ‘accusative’ pronouns forever – Sapir wrote about it (as a case of “language drift”), and Ed Klima, one of my favorite grad school professors, had worked on it and talked with us about it (we tried to figure out what kinds of rules would make ‘us’ and ‘me’ not get nominative in conjoined subjects while "I" and "we" as simple subjects are obligatorily marked nominative, and discussed similarities with French ‘disjunctive’ pronoun ‘moi’ vs. clitic subject 'je'). And it was the source of my oft-repeated anecdote about my son Morriss in 4th grade asking me to proofread a composition he had just written – it started out ‘Seth and I went to the mall’ and he pointed to ‘Seth and I’, and said to me “That’s how you spell “me and Seth”, right?”.
But none of that had prepared me for having it emerge in my own dialect. But there it was. And when I think about putting “We and our Red Sox buddies” instead, it sounds over-formal, doesn’t fit in the context of baseball buddies. So it looks like “us and …” has made the move from passive recognition to becoming an active part of my (most?) colloquial register, at least the baseball buddies register.